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A new cost-effective radiometer has been designed, built, and tested to measure direct normal solar irradiance (DNI). The proposed instrument for solar irradiance measurement is based on an optical fiber as the light beam collector, a semiconductor photodiode to measure the optical power, and a calibration algorithm to convert the optical power into solar irradiance. The proposed radiometer offers the advantage of separating the measurement point, where the optical fiber collects the solar irradiation, from the place where the optical power is measured. A calibration factor is mandatory because the semiconductor photodiode is only spectrally responsive to a limited part of the spectral irradiance. Experimental tests have been conducted under different conditions to evaluate the performance of the proposed device. The measurements confirm that the proposed instrument performs similarly to the expensive high-accuracy pyrheliometer used as a reference. [ABSTRACT FROM AUTHOR]

The non-scanning radiometer with short-wavelength (SW: 0.2–5.0 μm) and total-wavelength (TW: 0.2–50.0 μm) channels is the primary payload of the Integrated Earth–Moon Radiation Observation System (IEMROS), which is designed to provide comprehensive Earth radiation measurements and lunar calibrations at the L1 Lagrange point of the Earth–Moon system from a global perspective. This manuscript introduces a radiometer preflight calibration methodology, which involves background removal and is validated using accurate and traceable reference sources. Simulated Earth view tests are performed to evaluate repeatability, linearity, and gain coefficients over the operating range. Both channels demonstrate repeatability uncertainties better than 0.34%, indicating consistent and reliable measuring performance. Comparative polynomial regression analysis confirms significant linear response characteristics with two-channel nonlinearity less than 0.20%. Gain coefficients are efficiently determined using a two-point calibration approach. Uncertainty analysis reveals an absolute radiometric calibration accuracy of 0.97% for the SW channel and 0.92% for the TW channel, underscoring the non-scanning radiometer's capability to provide dependable global Earth radiation budget data crucial to environmental and climate studies. [ABSTRACT FROM AUTHOR]

A Moon-based radiometer can provide continuous measurements for the Earth's full-disk broadband irradiance, which is useful for studying the Earth's Radiation Budget (ERB) at the height of the Top of the Atmosphere (TOA). The ERB describes how the Earth obtains solar energy and emits energy to space through the outgoing broadband Short-Wave (SW) and emitted thermal Long-Wave (LW) radiation. In this work, a model for estimating the Earth's outgoing radiative flux from the measurements of a Moon-based radiometer is established. Using the model, the full-disk LW and SW outgoing radiative flux are gained by converting the unfiltered entrance pupil irradiances (EPIs) with the help of the anisotropic characteristics of the radiances. Based on the radiative transfer equation, the unfiltered EPI time series is used to validate the established model. By comparing the simulations for a Moon-based radiometer with the satellite-based data from the National Institute of Standards and Technology Advanced Radiometer (NISTAR) and the Clouds and the Earth's Radiant Energy System (CERES) datasets, the simulations show that the daytime SW fluxes from the Moon-based measurements are expected to vary between 194 and 205 Wm−2; these simulations agree well with the CERES data. The simulations are about 5 to 20 Wm−2 smaller than the NISTAR data. For the simulated Moon-based LW fluxes, the range is 251~287 Wm−2. The Moon-based and NISTAR fluxes are consistently 5~15 Wm−2 greater than CERES LW fluxes, and both of them also show larger diurnal variations compared with the CERES fluxes. The correlation coefficients of SW fluxes for Moon-based data and NISTAR data are 0.97, 0.63, and 0.53 for the months of July, August, and September, respectively. Compared with the SW flux, the correlation of LW fluxes is more stable for the same period and the correlation coefficients are 0.87, 0.69, and 0.61 for July to September 2017. [ABSTRACT FROM AUTHOR]

Objectives: Since there is only nadir radiometer onboard for the wide-swath altimetry, the wet tropospheric delay can only be corrected by models inside the cross-swath or substituted by the nadir radiometer measured data, which lead to the lower accuracy.Methods: In order to improve the accuracy of wet tropospheric correction (WTC) inside the cross-swath, an optimum interpolation method to fuse the nadir radiometer WTC is proposed, and it is verified by taken the SWOT (surface water and ocean topography) wide-swath altimeter as example. Results: Inside the cross-swath, when the ERA5 (ECMWF reanalysis 5th generation) data are used, the residual of WTC after correction by optimum interpolation method can be reduced by 40% compared with the nadir radiometer WTC substituted. When the simulated WTCs from the spectrum of radiometer measured WTCs are used, the residual of WTC after correction by optimum in⁃ terpolation method can be reduced by 80% in all latitude areas compared with the nadir radiometer WTC substituted.Conclusions: The optimum interpolation method has much better accuracy than the nadir radiometer WTC substituted in the case of high water vapor variability. [ABSTRACT FROM AUTHOR]

This study presents an original approach on how to generate a radiator with an emissivity less than one by using a conventional blackbody and a screen with a defined area density of holes. This is needed for the calibration of infrared (IR) radiometry, which is a very useful form of temperature measurement in industrial, scientific, and medical applications. One of the major sources of errors in IR radiometry is the emissivity of the surface being measured. Emissivity is a physically well-defined parameter, but in real experiments, it may be influenced by many factors: surface texture, spectral properties, oxidation, and aging of surfaces. While commercial blackbodies are prevalent, the much-needed grey bodies with a known emissivity are unavailable. This work describes a methodology for how to calibrate radiometers in the lab or in the factory or FAB using the "screen approach" and a novel thermal sensor dubbed Digital TMOS. The fundamental physics required to appreciate the reported methodology is reviewed. The linearity in emissivity of the Digital TMOS is demonstrated. The study describes in detail how to obtain the perforated screen as well as how to do the calibration. [ABSTRACT FROM AUTHOR]

This paper is a technical report describing the use of an open-source instrument called LANcube v2 to estimate a lighting devices inventory. The instrument has 5 color sensitive sensors, each on a face of a cube. The instrument can be mounted on a car roof to create a map of the artificial light at night while roaming the streets and roads. Based on the temporal variations of the detected signal on various cube’s faces, we developed a method of finding the approximate position in 3D of each source. The lamp spectral types can be determined relatively well thanks to the color balance of the raw Red (R), Green (G), Blue (B), and Clear (C) color bands. If one assumes a typical angular photometry of a source with respect to its location, it is possible to estimate roughly its current luminous flux. Such information allows us to build a lighting devices inventory of a territory. One advantage of that new method is that it can provide information about the private sources that are always excluded from public lighting inventories. We compared the inventory extracted with that new methodology with an in-situ lamp inventory made for two villages in Canada. This comparison allows us to emphasize the strengths and limitations of the method by comparing to the ground truth. We found that we were able to detect 99% of the sources with flux higher than 1000 lumen and located within 15 meters from the road. We also found that we generally overestimate the height of the devices by 21 to 51% depending on the lamp photometry. This overestimate surely reflects in an overestimate of the fluxes. Finally, we found that the proposed method is very efficient to recognize the spectral type of the devices with 99% of success. [ABSTRACT FROM AUTHOR]

Accurate information on tropical cyclone position, intensity, and structure is critical for storm surge prediction. Atmospheric reanalysis datasets can provide gridded, full coverage, long-term and multi-parameter atmospheric fields for the research on the impact of tropical cyclones on the upper ocean, which effectively makes up for the uneven temporal and spatial distribution of satellite remote sensing and in situ data. However, the reanalysis data cannot accurately describe characteristic parameters of tropical cyclones, especially in high wind conditions. In this paper, the performance of the tropical cyclone representation in ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis 5th Generation) is investigated and analyzed with respect to IBTrACS (International Best Track Archive for Climate Stewardship) during the period 2018–2020. Comparisons demonstrate that ERA5 winds significantly underestimate the maximum wind speed during the tropical cyclones (>30 m/s) compared to those provided by IBTrACS. An effective wind reconstruction method is examined to enhance tropical cyclone intensity representation in reanalysis data in 94 cases of 31 tropical cyclones 2018–2020. The reconstructed wind speeds are in good agreement with the SFMR (Stepped Frequency Microwave Radiometer) measured data and SMAP (Soil Moisture Active Passive) L-band radiometer remotely sensed measurements. The proposed wind reconstruction method can effectively improve the accuracy of the tropical cyclone representation in ERA5, and will benefit from the establishment of remote sensing satellite retrieval model and the forcing fields of the ocean model. [ABSTRACT FROM AUTHOR]

• Normal concentrations of ionized calcium in children differ from adults. • Radiometer instruments record lab results for all analytes independent of the order(s) placed. • Radiometer data can be used to apply exclusion criteria and calculate reference intervals. Measurement of ionized calcium (iCa) reflects bioavailable calcium and has significant utility in children. However, robust pediatric iCa reference intervals (RI) have not been well-established. In this study, we retrospectively calculated RI for iCa in a pediatric population by accessing archived data acquired on Radiometer instruments and applying stringent exclusion criteria. Data saved on 4 Radiometer ABL800 FLEX blood gas analyzers were queried. Exclusion criteria were applied based on information available from these instruments. iCa results were plotted and inflection points were visually identified. Following outlier removal and partition verification, age-specific RI were calculated using a nonparametric rank order approach from > 5,000 individuals. Finally, the stringency of the exclusion criteria was assessed by calculating RI from additional results in the dataset and comparing to existing in-house ranges. Six age-specific iCa partitions were established from 0 to 19 years. Relative to adults, wider ranges for the central 95th percentile were observed early in life that progressively narrowed with increasing age and approached adult concentrations by 2.5 years. Analysis of concurrent data for sodium and creatinine in the dataset suggest the applied exclusion criteria reduced the likelihood of including results from acutely-ill children. Normal concentrations of iCa in children are more variable than adults. Observed differences may reflect the transition from maternally supplied calcium to nutritional sources, the maturation of calcium homeostatic mechanisms, and/or the need for calcium for growth/development. This study also demonstrates the feasibility and advantages of using data archived on Radiometer analyzers to establish pediatric RI. This approach enables rapid, cost-effective evaluation of large datasets and may be a feasible option when prospective or detailed retrospective analyses are not possible. [ABSTRACT FROM AUTHOR]

The Earth's radiation budget (ERB), measured at the top of the atmosphere (TOP), quantifies the radiation imbalance between the Earth–atmosphere system and space. The ERB's measurement accuracy depends on the observation system's design and calibration technology. Fitting regional scanning data from polar satellite payloads is the most common way to obtain the global radiation budget. Additionally, the radiometers are calibrated by onboard stable radiation sources. We propose a new ERB radiometer operating at the Lagrange L1 point of the Earth–Moon system, which has the characteristic of observing the Earth and Moon on a hemispheric spatial scale. Hence, earth-integrated radiation can be measured directly. Furthermore, the Moon is used as a natural source for on-orbit calibration, and the attenuation of the instrument is monitored and corrected through periodic observations. This paper presents the concept of the radiometer and focuses on the design and analysis of the radiometer's observation systems based on optical design and stray radiation suppression. The results show that the system has good imaging quality. The external stray radiation suppression reached an order of 10−8, and the thermal stray radiation can be eliminated by temperature control and compensation. The radiometer will provide long-term integrated ERB data. [ABSTRACT FROM AUTHOR]

This paper presents measurements using a dual-polarised radiometer operating at 93 GHz to detect ice or water on asphalt in laboratory conditions. The brightness temperatures of both H and V polarizations were measured for a dry surface, liquid water, and ice on asphalt at observation angles of 50° and 56°. The results presented in this paper demonstrate that the studied road conditions can be identified by the radiometer. The measurements are compared with a model and surface parameters, such as dielectric constant and roughness are fitted and compared to reference values. The experiments and results, described in this article, are the first steps towards the future installation of a polarimetric sensor on a moving vehicle for traffic safety. [ABSTRACT FROM AUTHOR]

The Temporal Experiment for Storms and Tropical Systems Technology Demonstration (TEMPEST-D) instrument is a five-frequency millimeter-wave radiometer operating from 87 to 181 GHz. The cross-track scanning radiometer has been operating on a 6U CubeSat in low Earth orbit since September 5, 2018. The direct-detection architecture of the radiometer reduces its mass and power consumption by eliminating the need for a local oscillator and mixer, also reducing system complexity. The instrument includes a scanning reflector and ambient calibration target. The reflector rotates continuously to scan the antenna beams in the cross-track direction, first across the blackbody calibration target, then toward the Earth over the full range of incidence angles, and finally to cosmic microwave background radiation at 2.73 K. This enables precision end-to-end calibration of the millimeter-wave receivers during every 2-s scan period. The TEMPEST-D millimeter-wave radiometers are based on 35-nm indium phosphide (InP) high-electron-mobility transistor (HEMT) low-noise amplifiers. This article describes the instrument and its characterization prior to launch. [ABSTRACT FROM AUTHOR]

We present a co-designed Dicke switch and low-noise amplifier (LNA) in which the switch incorporates a transformer-based topology and serves as the input matching network of the LNA. This topology is configured to minimize the amplifier gain mismatch between the two switching states caused by process variations while providing a low noise figure (NF). The circuit is implemented in a 0.13-μm SiGe BiCMOS technology, and it achieves more than 20-dB gain and minimum NF values of 4.5 and 0.58 dB at 300 and 20 K, respectively. It consumes a dc power of 15 mW. The front-end switch presents a peak isolation of 17 dB, and the input return loss is better than 15 dB across 45–70 GHz. A noise source is also coupled to the front-end circuitry to enable on-chip calibration. The noise performance and reliability of several on-chip p-n junctions were characterized, and the one with the highest excess noise ratio was coupled to the front-end circuitry. To the best of our knowledge, the lowest NF of an integrated switch and LNA at V-band frequencies is achieved in the present work, along with the first reliability study of on-chip noise sources in a SiGe BiCMOS technology. [ABSTRACT FROM AUTHOR]

• Ground based radiometer has been used to calculate cloud attenuation. • Significant cloud attenuation has been observed over Kolkata in monsoon at 30 GHz. • August shows the worst month scenario due to high value of LWP. • Cloud attenuation has been compared with rain attenuation. The objective of this study is to investigate cloud attenuation at 30 GHz frequency using ground-based microwave radiometric observations at a tropical location, Kolkata. At higher frequencies and lower elevation angles, cloud attenuation is of major concern at a tropical location. The location experiences high value of liquid water path (LWP), which is responsible for cloud attenuation, during the Indian summer monsoon (ISM) and pre-monsoon season. Significant amount of cloud attenuation has been observed during monsoon season at 30 GHz. Two years observations of exceedance probability of cloud attenuation and worst month statistics are presented. The variation of cloud attenuation with frequencies for different elevation angles has also been investigated. The seasonal and diurnal patterns of cloud attenuation are examined. Cloud attenuation, inferred from radiometric measurements before rain commencement, has been compared to rain attenuation at Ku-band. Exceedance probabilities of cloud and rain attenuation have been compared. [ABSTRACT FROM AUTHOR]

In the application of ultraviolet (UV light), it is necessary to obtain reliable information on UV effectiveness, i.e., one should know the fluence reached by microorganisms or the dose absorbed by chemicals. For this reason, a collimated beam apparatus (CBA) is widely used. International Ultraviolet Association (IUVA) recommends a protocol on CBA in which the beams are assumed to be collimated. In this work, focusing on the fact that so-called collimated beams are not really collimated, a mathematical model for CBA is established, and the influencing factors and specifications of CBA are rigorously analyzed. The aperture type not only has high measurement accuracy, but its specific characteristics are also suitable for the calibration of radiometers in chemical actinometers. The suitable conditions for the calibration are also investigated. [ABSTRACT FROM AUTHOR]

Crookes radiometers have been the subject of numerous theoretical, numerical, and experimental studies because of the complicated forces they exhibit as well as their potential applications to light sensing and actuation. The majority of these studies have focused on classical radiometers, which function under low vacuum pressures. In contrast, here we report a radiometer with microengineered vanes that rotates at atmospheric pressure. Its functionality at pressures thousands of times higher than previous light mills is due to unique attributes of the nanocardboard that forms its vanes: 1) the extremely low areal density (0.1 mg/cm2) of nanocardboard reduces the vane masses by two orders of magnitude; 2) its lower thermal conductivity allows a greater cross-vane temperature difference; and 3) its microchannels dramatically increase the thermal transpiration flow that drives the rotation. Intriguingly, the experimentally observed rotation speeds are substantially higher than those theoretically expected. Our device demonstrates new possibilities for micromanipulation, propulsion of aerial vehicles, and light-powered generators. [2020-0165] [ABSTRACT FROM AUTHOR]

With the help of Ground Based seven channel K-Band humidity profiling radiometer, humidity at different height levels from 0 to 10 Km from ground has been obtained for two years from 2016 to 2017. Radiometer based zenith attenuation has been retrieved for the 20-30 GHz band which have been compared with ITU-R proposed attenuation estimation due to absorption by gases. ITU-R estimation has been found to underestimate zenith attenuation for tropical high rainfall region like Umiam. The Mean Atmospheric Temperature has been estimated from ground observations and Zenith Radiometer Attenuation through linear regression equations. Additionally, water vapour scale height has been estimated from zenith attenuation and surface meteorological parameters. Total water vapour has been also obtained from this and compared with Total water vapour estimated from IWV retrievals by radiometer. A regression relation has been found between IWV and 22.24 GHz brightness temperature obtained from Radiometer. [ABSTRACT FROM AUTHOR]

Using internally consistent albedo, aerosol, cloud, and surface data from the Multiangle Imaging Spectroradiometer (MISR) instrument onboard the Terra satellite, top-of-atmosphere (TOA) spectral albedo change (dα) in the presence of aerosols over land is estimated and its dependence on aerosol and surface properties is analyzed. Linear regressions between spectral TOA albedo and aerosol optical depth (AOD) for different surface types are examined to derive the aerosol-free TOA albedo. MISR surface BiHemispherical Reflectance (BHR) values are used to differentiate surface types. We find relatively high correlations between spectral TOA albedo and AOD for BHR-stratified data in 2° × 2° grid cells. The global mean values of cloud-free dα over land for June–September 2007 are estimated to be 0.018 ± 0.003 (blue), 0.010 ± 0.003 (green), 0.007 ± 0.003 (red), and 0.008 ± 0.006 (near-infrared). Individual regions show large variations from these values. Global patterns of dα are determined mainly by AOD and aerosol radiative efficiency. Large positive values of dα are observed over regions with high aerosol loading and large single-scattering albedo, where the aerosol scattering effect is dominant. The presence of light-absorbing aerosols reduces aerosol radiative efficiency and dα. Surface reflectance influences both aerosol scattering and absorbing effects. Generally, the aerosol radiative efficiency decreases with increasing BHR. We also examined dα-AOD correlations over different vegetation types. We find the smallest dα values are over needleleaf forests and shrublands, whereas the largest values are over cropland and barren regions. The aerosol radiative efficiencies are lowest over needleleaf forests and barren regions and highest over grasslands and croplands.

Satellite fire products have the potential to construct inter-annual time series of fire activity, but estimating area burned requires considering biases introduced by orbiting geometry, fire behavior, and the presence of clouds and smoke. Here we evaluated the performance of fire counts from the Advanced Thermal Scanning Radiometer (ATSR) for the boreal forest region using area burned information from other sources. We found ATSR detection rate varied between regions and different years, being higher during large fire years than during small fire years. The results show ATSR fire counts do not represent an unbiased sample of fire activity, and independent validation may be required prior to using this data set in studies of global emissions from biomass burning.

Abstract The current thermoelectric solar tower plants demand the measure of high solar irradiance on the receiver. Its measure would facilitate the operation of the plant and would contribute to a greater receiver security. Currently, solar tower plants do not have a flux measurement system in their receiver as it is not considered in their design. The inclusion of the flux measurement system in its design phase would facilitate its incorporation and correct operation. Instead, infrared temperature measurement systems are used to infer the irradiance on the receiver. This procedure is not suitable since the delay between the irradiance and the temperature in the receiver can reach a few minutes depending on the materials, the transfer fluid, the operating conditions and the meteorological variables. Traditional flux measurement methods, used during the evaluation of small solar receiver prototypes, turn to moving parts that do not extrapolate to large receivers of commercial solar tower plants due to scaling problems. On the other hand, the use of mobile elements, which interact with the concentrated solar radiation directed towards the receiver, would negatively affect the daily operation of the plant. This work presents a simple method that allows characterizing a large target and quantifying its degree of homogeneity and diffusivity. With favourable information about receiver diffusivity, a way of proceeding to measure directly high solar irradiance on the surface of the receivers of solar tower plants without including moving parts is presented. This measurement system would consist of a digital camera and a radiometer. Highlights • Procedure to measure directly high solar irradiance on the receiver surface. • This measurement system consists of a digital camera and a radiometer. • Characterization of a large target and quantification of its degree of diffusivity. [ABSTRACT FROM AUTHOR]

A new multilayer (ML) cloud detection algorithm based on three shortwave infrared (SWIR) and two longwave infrared (LWIR) channels is developed and applied to the Visible Infrared Imager Radiometer Suite (VIIRS) onboard the Suomi-NPP satellite. The algorithm identifies ML clouds, i.e., ice clouds overlying water clouds, based on satellite multispectral observations in the 1.38, 1.6, 2.25, 8.5, and 11 μm channels. We perform synthetic radiative transfer simulations to understand the sensitivities of the aforementioned channels on ML and single-layer (SL) clouds. Active CALIOP observations are used to evaluate the algorithm. Compared with the collocated CALIOP results, the algorithm can determine SL and ML clouds correctly with success rates of approximately 80% and 60%, respectively, and has similar performance to that of the current MODIS operational ML cloud detection algorithm. The misclassification of ML clouds as SL clouds is primarily caused by thin ice clouds that are practically undetectable using LWIR tests. Furthermore, the algorithm is extended to analyze data from radiometers onboard the geostationary Himawari-8 and FengYun-4A satellites, and results similar to those of VIIRS are obtained. • A new algorithm for multilayer cloud detection is developed for VIIRS radiometer. • Accurate radiative transfer is performed for model understanding and development. • The model is evaluated using collocated MODIS and CALIOP observations. • It is extended for multilayer cloud detection of two geostationary radiometers. [ABSTRACT FROM AUTHOR]

A low noise, high gain, stable radiometer front-end is presented for non-invasive tissue thermometry using custom designed narrow band low noise amplifiers (LNAs) and band pass filter (BPF) with 1.3 GHz centre frequency and − 20 dB pass band of 332 MHz. The fabricated LNAs have >15 dB gain, unconditional gain stability and noise figure (NF) < 1.45 dB in the pass band. The maximum insertion loss of the BPF is <1 dB over 1.2-1.4 GHz with 50 dB suppression in the surrounding communication bands. The cascaded radiometer front-end has measured gain of 45-50 dB, NF < 1.75 dB in the pass band and > 30 dB suppression in the adjacent personal communication bands. The Allan deviation of the total power radiometer indicates long term system stability and presence of Gaussian thermal noise for integration time, . Radiometer measurements of a matched load at room temperature for indicate acceptably low influence of external electromagnetic interference (EMI) and system noise equivalent temperature of 145 K. The brightness temperature measured by the total power radiometer using a resonant slot antenna demonstrates the ability to detect a 0.3°C change in the test load temperature with better than 0.1°C accuracy. [ABSTRACT FROM AUTHOR]

Conventional scatterometer wind retrieval has been proved effective for low and moderate wind conditions. Under high wind conditions, especially for typhoons, the air–sea interactions are fierce, and usually the sea surface backscattering is complicated by rain, leading to degraded scatterometer wind quality. Under such circumstances, radiometers in different frequencies can provide information of rains and the complex air–sea interface. In this paper, an artificial neural network (ANN) was employed to combine the observations of the two sensors onboard HY-2A satellite: radiometer and scatterometer (HSCAT) to achieve wind field retrieving under typhoon conditions. The ANN was trained by using global/regional assimilation and prediction system (GRAPES) wind field data as true values. The established network is then verified by an independent dataset excluded from the training data. It is shown that the wind speeds and directions retrieved from the ANN are better than those of the operational HSCAT products as compared to GRAPES winds. Further comparison with the H*Wind product proves that the proposed ANN is effective in terms of high wind field retrieval. The research of this paper provides a nice reference for the typhoon wind retrieval from the HY-2A satellite and for the data processing of the coming HY-2 satellite series. [ABSTRACT FROM AUTHOR]

A high-resolution dual-band terahertz (THz) radiometer was designed to measure vertical distributions of chemical elements in the middle atmosphere of the Tibetan Plateau. A forward simulation, which always should be conducted firstly for the development of a matching retrieval algorithm, has not been done before. We use two radiative transfer models, ARTS and AM, to simulate the water vapor, ozone and carbon monoxide spectra on the plateau based on the spectral design of the THz radiometer. The emission line characteristics of the three gases in this spectral band are identified. Reasons for the differences in the spectral simulations between the two models are analyzed for individual gases. The impact of several different spectral parameter settings on the simulations are evaluated through a series of sensitivity experiments. This study suggests that the ARTS is more suitable for the development of the THz radiometer retrieval algorithm. An optimal parameter setting of the ARTS for the three elements are given. [ABSTRACT FROM AUTHOR]

This paper describes a novel cost effective narrow-beam radiometer what was designed to measure incident heat flux at a specific location in high temperature and high pressure combustor. Beyond the radiometer the whole measurement assembly contains a water cooled plate for cold background, a high pressure window transparent for visible and IR radiation and a radiometer position/angle adjustment tool. The thermopile based radiometer measures the total heat radiation in a wavelength range of 0.6–8 µm. A special view tube was developed for decreasing the view angle to 0.35°, what angle was dictated by the dimensions of the combustor and the associated port sizes. Calibration curves were measured using a high temperature black body calibrator and the uncertainty of the measurement was evaluated. Although the presented radiant heat flux measurement method was developed for a specific combustor, it can be easily implemented for various combustion applications as well. [ABSTRACT FROM AUTHOR]

The Mars Environmental Dynamics Analyzer (MEDA) is a suite of environmental sensors onboard NASA’s Mars 2020 mission. The Thermal InfraRed Sensor (TIRS), developed at Centro de Astrobiología of Spain, is one of the six sensors comprising MEDA, and it will measure the net thermal infrared radiation and reflected solar radiation at the surface, as well as the atmospheric and surface skin temperatures using five different channels. In combination with MEDA's other sensors, TIRS will allow the quantification of the surface energy budget and the determination of key geophysical properties of the terrain such as the albedo and thermal inertia. Here we present a general description of the TIRS, its channels scientific requirements, and the mechanical and thermal design. Then, a detailed sensor mathematical model and a sensitivity analysis to model uncertainties are described. Some characterization test results to model parameters identification are included. Finally, accuracy and resolution calculus for each channel versus operational temperature is presented. The calculus is performed based on sensitivity equations, the practical tests results and the estimated values for different uncertainty sources. [ABSTRACT FROM AUTHOR]

Aerosol is an important part of the earth-atmosphere system. It can directly and indirectly influence solar radiation and then affect the energy balance of earth-atmosphere system. AERONET, as the largest ground-based observation network, provides multiparameters of aerosol from more than 600 hundred sites using sun-sky radiometer, which contains 9 channels from 340 nm to 1640 nm. Among which, 1020 nm channel is greatly influenced by the temperature. In this paper, a new correction method of 1020 nm band is introduced. The new method transfers the temperature correction coefficient of the master radiometer to the comparative one. The filed calibration experiment shown that the temperature correction coefficient obtained by this method is close to the result from the temperature controlled chamber, and the difference is about 2.1%. This new method is easy-to-use, and its accuracy is comparable to the standard one. It is more applicable for large-scale instrument calibration. In principle, this method is applicable to all bands of the sun-sky radiometer. [ABSTRACT FROM AUTHOR]

A compact Q-band waveguide-to-microstrip transition for UAV(Unmanned Aerial Vehicle) radiometer applications is presented. The key features of this transition are simplicity, compactness, easy matching, and lower sensitivity to the dimensions and fabrication tolerances. The simple E-plane patch-type design is insensitive to the backshort cavity enclosure and misalignment between the waveguide and microstrip substrate. The primary parameters are optimized using a three-dimensional(3D) electromagnetic simulator(ANSYS HFSS). It exhibited better than 20-dB return loss at mid-band frequencies with less than 1-dB insertion loss for the back-to-back transition, and a return loss better than 15 dB over the frequency range of 36 GHz to 42 GHz. [ABSTRACT FROM AUTHOR]

The paper investigates the theory of operation of a passive millimeter-wave seeker sensor using a fast electronic sequential-lobing technique and the experimental validation obtained through laboratory trials. The paper analyzes in detail the theoretical performance of a difference channel sensor and a pseudo-monopulse sensor deriving agile formulas for the estimation of target angular tracking accuracy and the subsequent experimental validation. [ABSTRACT FROM AUTHOR]

A correlation analysis of the model calculations and experimental measurements of wind-speed sensitivity of a rough sea-surface microwave emission at a frequency of 37.5 GHz are presented. The field data used in the research were collected over 3 years in the summer and autumn periods at the oceanographic platform of the Marine Hydrophysical Institute, Russian Academy of Sciences (RAS). A hypothesis about a significant correlation between the model calculations and experimentally measured sea-surface emission ability caused by wind forcing was formulated and tested to reveal this correlation. An evaluation of the discrepancy between the model and experimental data has been performed by an analysis of residuals. Our studies have shown that among the selected models not a single one adequately describes the experimental data. [ABSTRACT FROM AUTHOR]

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Moderate Resolution Imaging Spectroradiometer (MODIS) reflective solar bands (RSBs) are calibrated on-orbit using a solar diffuser (SD) with its degradation tracked by an onboard SD stability monitor (SDSM). The SDSM has nine detectors with wavelengths from 0.41 to 0.94 \mu \textm . It is operated during each scheduled SD calibration event, making alternate observations of the sun and the SD. Due to erroneous design parameters, which led to the misalignment of the key elements in the SDSM, there are significant ripples in the sun view responses as the solar viewing angle changes. At the mission beginning, the effect of the ripples was eliminated by normalizing each SDSM detector response to the response of detector 9 (D9) at 0.94 \mu \textm , assuming that D9 had no degradation. However, D9 degradation increases over MODIS operation times. Degradation of up to 2% has recently been observed in D9 for the Terra MODIS. A newly implemented approach reduces the sun view ripples using a lookup table constructed using SDSM data carefully selected from a short period early in the mission lifetime. In this paper, we provide an overview of different approaches that have been applied over the years by the MODIS Characterization Support Team to track the on-orbit SD degradation. We evaluate the overall SD and SDSM on-orbit performance for both Terra and Aqua MODIS, as well as the impact on the MODIS RSB calibration uncertainty. [ABSTRACT FROM PUBLISHER]

This paper describes the analysis, design, and characterization of a high-sensitivity millimeter-wave total-power radiometer front-end integrated into a 0.25- \mu \textm SiGe:C BiCMOS technology. This prototype is composed of a two cascode stage low-noise amplifier (LNA) and a voltage-driven common-emitter square-law detector. The LNA is interfaced to the detector through a low transformation ratio (i.e., high-impedance node) to achieve an efficient wideband signal transfer. The front end achieves both a low $1/f$ -noise corner and a low noise-equivalent power (NEP) by combining a large area, high resistive value load resistor together with a minimum size heterojunction bipolar transistor. At 56 GHz and optimum bias, the prototype provides a 61-MV/W responsivity which combined with a 194-nV/ $\surd $ Hz white noise level result in a 3.2-fW/ $\surd $ Hz NEP when the input power is modulated with a frequency above the 30-Hz flicker noise corner. The achieved 3-dB NEP bandwidth is 6 GHz. [ABSTRACT FROM PUBLISHER]

The MASCOT radiometer MARA is a multi-spectral instrument which measures net radiative flux in six wavelength bands. MARA uses thermopile sensors as sensing elements, and the net flux between the instrument and the surface in the $18^{\circ }$ field of view is determined by evaluating the thermoelectric potential between the sensors' absorbing surface and the thermopile's cold-junction. MARA houses 4 bandpass channels in the spectral range of 5.5-7, 8-9.5, 9.5-11.5, and 13.5-15.5 μm, as well as one long-pass channel, which is sensitive in the $>3~\upmu \mbox{m}$ range. In addition, one channel is similar to that used by the Hayabusa 2 orbiter thermal mapper, which uses a wavelength range of 8-12 μm. The primary science objective of the MARA instrument it the determination of the target asteroid's surface brightness temperature, from which surface thermal inertia can be derived. In addition, the spectral bandpass channels will be used to estimate the spectral slope of the surface in the thermal infrared wavelength range. The instrument has been calibrated using a cavity blackbody, and the temperature uncertainty is 1 K in the long pass channel for target temperatures of $>173~\mbox{K}$ . Measurement uncertainty in the spectral bandpasses is 1 K for target temperatures above 273 K. [ABSTRACT FROM AUTHOR]

A robust physics-based combined active–passive (C-AP), or active–passive, surface soil moisture and roughness estimation methodology is presented. Soil moisture and roughness retrieval is performed via optimization, i.e., minimization, of a joint objective function, which constrains similar resolution radar and radiometer observations simultaneously. A data-driven and noise-dependent regularization term has also been developed to automatically regularize and balance corresponding radar and radiometer contributions to achieve optimal soil moisture retrievals. It is shown that in order to compensate for measurement and observation noise, as well as forward model inaccuracies, in C-AP estimation, surface roughness can be considered a free parameter. Extensive Monte Carlo numerical simulations and assessment using field data have been performed both to evaluate the algorithm’s performance and to demonstrate soil moisture estimation. Unbiased root mean squared errors range from 0.18 to 0.03 cm3/cm3 for two different land-cover types of corn and soybean. In summary, in the context of soil moisture retrieval, the importance of consistent forward emission and scattering development is discussed and presented. [ABSTRACT FROM PUBLISHER]

Manufacture and in-service assessment of composite materials can be challenging since there is, yet, no standard method for testing them. Nevertheless, regular inspection is necessary to maintain the structural integrity. This paper describes a nondestructive, broadband noise mapping method that uses a millimeter-wave radiometer to detect defects in composite materials. The $W$ -band system is configured for transmission mode measurement in which an amplified photonic source illuminates a glass fiber reinforced polymer containing machined defects. A high sensitivity radiometer is used for imaging the sample. The radiometer consists of a Schottky diode-based frequency tripler and a fundamental mixer. [ABSTRACT FROM AUTHOR]

A multichannel radiometer frontend, which can improve the radiometer sensitivity and utilization of the frequency band dramatically, is proposed based on the principle of bandwidth synthetic technology. The multichannel radiometer, called multichannel bandwidth synthetic radiometer (MCBWSR), consists of multiple conventional radiometer channels, and the frequency bands of all the channels are synthesized by the bandwidth synthesizer before the detector. The synthesized bandwidth of the synthesizer can reach a maximum of the sum of all the bandwidths. The operating frequency can also be selected flexibly using the frequency conversion technology. An analysis of the sensitivity \Delta Tsyn of the MCBWSR is deduced in terms of the conventional single-channel radiometer sensitivity \Delta Ti . The relationship of sensitivity between the conventional single-channel radiometer and MCBWSR is validated using an RF simulator. To verify the analysis, three experiments are implemented on a direct detection radiometer, a heterodyne radiometer, and a dual-channel bandwidth synthetic radiometer (DCBWSR) receiver, respectively. The experimental results are presented, and the sensitivity among them is compared. These results indicate that the DCBWSR can improve the sensitivity by about 1/\sqrt 2 , which is consistent with the theoretically calculated results. Compared with the conventional radiometers, the MCBWSR has the advantages of higher sensitivity, lower power consumption, and integration. [ABSTRACT FROM AUTHOR]

In this paper, we introduce the combined active/passive (CAP) data product for the Soil Moisture Active Passive mission. We develop the algorithms for a radiometer-only salinity product, a radar-only vector wind product, and a CAP vector wind and salinity product. We show that the performance of the radiometer-only salinity product nears but is still inferior to the Aquarius salinity accuracy performance when aggregated on a monthly timescale. Then, we show that the radar-only vector wind product has reasonable accuracy away from the nadir track while suffering from inadequate measurement geometry in the middle of the swath. Finally, we demonstrate that the CAP salinity and vector wind performance is superior to individual algorithms and provides wind vectors nearly as good as RapidScat for low-to-moderate winds and possibly superior to traditional scatterometers for wind speeds larger than 12.5 m/s. [ABSTRACT FROM PUBLISHER]

The global measurement of sea-surface salinity and more precise measurements of soil moisture from space has been enabled by L-band observations from the Soil Moisture and Ocean Salinity (SMOS) mission, the Aquarius mission, and the Soil Moisture Active Passive (SMAP) mission. These measurements are key components of the global water cycle and the ability to resolve climate scale variations in these variables is extremely valuable for improved understanding of how the hydrologic cycle varies in a changing climate system. It is therefore imperative that the radiometer systems making these measurements be calibrated to remove any spurious instrument temporal drifts. In this paper, models are developed over Antarctica and rainforest regions to track the gain and offset drifts in spaceborne L-band radiometer brightness-temperature (TB) measurements. The Antarctica region is found to be best for tracking small variations (0.1 K over 10 days) for vertically polarized observations near the Brewster angle. The rainforest regions are found to be best for tracking longer term variations ($ > $60 days) in all channels, due to larger uncertainty in the surface temperature knowledge, and excellent for tracking shorter term variations between channels ($ < $10 days). These reference regions were used to separate a long-term gain drift and a quasi-monthly offset variation in the Aquarius radiometer. These observations eventually led to the characterization of the root cause for the drift and are contributing to improved correction methods based on models for the hardware behavior. [ABSTRACT FROM PUBLISHER]

High-resolution estimation of thermodynamic properties in the atmosphere can help to predict and mitigate meteorological disasters, such as local heavy rainfall and tornadic storms. For the purposes of short-term forecasting and nowcasting of severe storms, we propose a novel ground-based measurement system, which observes the intensity of atmospheric radiation in the microwave range. Our multi-band receiver system is designed to identify a rapid increase in water vapor before clouds are generated. At frequencies between 20 and 30 GHz, our system simultaneously measures water vapor as a broad absorption peak at 22 GHz as well as cloud liquid water. Another band at 50-60 GHz provides supplementary information from oxygen radiation to give vertical profiles of physical temperature. For the construction of this cold receiver system, novel technologies originally developed for observations of cosmic microwave background radiation were applied. The input atmospheric signal is amplified by a cold low-noise amplifier maintained below 10 K, while the spectrum of this amplified signal is measured using a signal analyzer under ambient conditions. The cryostat also contains a cold black body at 40 K to act as a calibration signal. This calibration signal is transported to each of the receivers via a wire grid. We can select either the atmospheric signal or the calibration signal by changing the orientation of this wire. Each receiver can be calibrated using this setup. Our system is designed to be compact ( $$<$$ 1 m $$^{3}$$ ), with low power consumption ( $$\sim $$ 1.5 kW). Therefore, it is easy to deploy on top of high buildings, mountains, and ship decks. [ABSTRACT FROM AUTHOR]

The objective of the NASA Soil Moisture Active Passive (SMAP) mission is to provide global measurements of soil moisture and freeze/thaw states. SMAP integrates L-band radar and radiometer instruments as a single observation system combining the respective strengths of active and passive remote sensing for enhanced soil moisture mapping. Airborne instruments are a key part of the SMAP validation program. Here, we present an airborne campaign in the Rur catchment, Germany, in which the passive L-band system Polarimetric L-band Multi-beam Radiometer and the active L-band system F-SAR of DLR were flown simultaneously on six dates in 2013. The flights covered the full heterogeneity of the area under investigation, i.e., the main land cover types and all experimental monitoring sites. Here, we used the obtained data sets as a test bed for the analysis of three active–passive fusion techniques: 1) estimation of soil moisture by passive sensor data and subsequent disaggregation by active sensor backscatter data; 2) disaggregation of passive microwave brightness temperature by active microwave backscatter and subsequent inversion to soil moisture; and 3) fusion of two single-source soil moisture products from radar and radiometer. Results indicate that the regression parameters $\beta$ are dependent on the radar vegetation index. The best performance was obtained by the fusion of radiometer brightness temperatures and radar backscatter, which was able to reach the same accuracy as single-source coarse-scale radiometer soil moisture retrieval but on a higher spatial resolution. [ABSTRACT FROM AUTHOR]

A radiometer operating between 50 MHz and 26.5 GHz and consisting of microwave channels all with a low-noise amplifier (LNA) was established. Microwave switches were used to select an appropriate channel according to measurement frequency. The effect of variations both in input and output reflection coefficients on LNA gain was investigated. To keep the change in the gain of the LNA at minimum, the LNA output was terminated with a load whose impedance was equal to that of matched load. This technique gives the opportunity of full-band noise measurements of noise sources with one total power radiometer. The performance of the overall radiometer was tested. The difference in excess noise ratio (ENR) between the experimental results and actual values was found between -0.32 dB and 0.30 dB with an expanded uncertainty between 0.13 dB and 0.34 dB (k = 2). The results illustrate the validity of the full-band radiometer for determining ENR. [ABSTRACT FROM AUTHOR]

To obtain the vertical temperature profile of the thermal skin layer on the aqueous side of the ocean–atmosphere interface from radiance measurements of hyperspectral infrared radiometers, regularization methods are used to address the nonlinearity and ill-conditioning of the inverse problem associated with the retrieval. This paper demonstrates the truncated singular value decomposition regularization technique on field data sets obtained from the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI). The M-AERI takes highly accurate and spectrally resolved radiance measurements in the infrared, which allows for the sensing of temperature values within thermal skin layer depths of less than 1 mm below the ocean surface. Results showed temperature inversions found in the solution, but these are deemed unphysical, based on previous tests on synthetic data and by a scaling analysis using the Rayleigh number, which are presented here. The importance of sea surface emissivity for performing the atmospheric correction to M-AERI measurements to derive surface emissivity spectra is also discussed. The retrieved profiles exhibit a smooth exponential-like structure that agrees well with theory. [ABSTRACT FROM PUBLISHER]

To eliminate the non‐uniformity response of integrating sphere detector, which is brought by the back surface of the measured main aperture of the solar irradiance absolute radiometer serving as a part of the integrating sphere wall in effective area method, a correction optical model is designed to tackle the issue in TracePro program. By simulations, the radiant flux responded by the integrating sphere detector is given. Then the curve of the relative change about the radiant flux is deduced and the experiment measurement data are corrected on the basis of relative change curve. Eventually, the uncorrected and the corrected main aperture areas are calculated. Within a series of repeated measurements, the relative uncertainties of the uncorrected results and the corrected results are both 7 × 10−5 (n = 7). The relative uncertainty of the differences between the raw results and corrected results is 9.65 × 10−5 which proves that the optical model can evaluate the deviation, efficiently. [ABSTRACT FROM AUTHOR]

A ground based microwave profiling radiometer has been operational in the Snowy Mountains in south eastern Australia and was used to build a limited three year data set of supercooled liquid water (SLW). Satellite observations (MODIS) of cloud-top thermodynamic phase suggest that SLW commonly occurs over the Snowy Mountains during the winter months and at much higher rates compared to other mountain ranges such as the Sierra Nevada. The radiometer was able to confirm the high frequency of occurrence of SLW at 53% of the time (April-September) and the observations were consistent with MODIS. Path integrated liquid water amounts observed from the radiometer were compared to those from MODIS, although the radiometer tended to observe significantly more liquid water than MODIS. SLW was documented and assigned to synoptic types with 43.0% of total SLW attributed to “cutoff lows" (equatorward of 45°S) and 42.2% were assigned to “embedded lows". [ABSTRACT FROM AUTHOR]