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Adaptive filtering and channel estimation techniques are applied to laser based ranging systems that utilize wide-band intensity modulation to measure the range and reflectivity of underwater objects. The proposed method aims to iteratively learn the frequency dependent characteristics of the underwater environment using a frequency domain adaptive filter, which results in an estimate for the channels optical impulse response. This work presents the application of the frequency domain adaptive filter to simulated and experimental data, and shows it is possible to iteratively learn the underwater optical channel impulse response while using Hybrid Lidar/Radar techniques.

Polarimetric characteristics of light from ocean water in combination with standard remote sensing reflectance provide important information about water constituents; they are useful in retrieval of additional water parameters like attenuation-to-absorption ratio and attenuation coefficients and/or establishing additional constraints for retrieval algorithms. The Stokes vectors of light above and below the water surface, which fully represent polarimetric characteristics of water leaving radiance, strongly depend on the particle size distribution and related Mueller matrices of water particulates. In this work we investigate the effect of various hydrosol mixtures of chlorophyllous particles on the polarized light field. The Stokes vectors of scattered light and the degree of polarization (DOP) are generated as outputs of vector radiative transfer simulations for various water compositions. Mie theory as well as T-matrix approaches are used for the generation of scattering matrices. The impact of their variability on the Stokes vectors of polarized light is analyzed.

Methods of artificial intelligence are a good solution for weather phenomena forecasting. They allow to process a large amount of diverse data. Recirculation Neural Networks is implemented in the paper for the system of thunderstorm events prediction. Large amounts of experimental data from lightning sensors and electric field mills networks are received and analyzed. The average recognition accuracy of sensor signals is calculated. It is shown that Recirculation Neural Networks is a promising solution in the forecasting of thunderstorms and weather phenomena, characterized by the high efficiency of the recognition elements of the sensor signals, allows to compress images and highlight their characteristic features for subsequent recognition.

We describe the development of a centimeter-scale resolution simulation framework for a theoretical tree canopy that includes rainfall deposition, evaporation, and thermal infrared emittance. Rainfall is simulated as discrete raindrops with specified rate. The individual droplets will either fall through the canopy and intersect the ground; adhere to a leaf; bounce or shatter on impact with a leaf resulting in smaller droplets that are propagated through the canopy. Surface physical temperatures are individually determined by surface water evaporation, spatially varying within canopy wind velocities, solar radiation, and water vapor pressure. Results are validated by theoretical canopy gap and gross rainfall interception models.

Synthetic aperture radar (SAR) uses sensor motion to generate finer spatial resolution of a given target area. In this paper we explore the theoretical potential of quantum synthetic aperture quantum radar (QSAR). We provide theoretical analysis and simulation results which suggest that QSAR can provide improved detection performance over classical SAR in the high-noise low-brightness regime.

The values of the unwrapped phase produced by interferometric pairs can be parameterized for phase components, such as height, atmospheric path delay and deformation term, and estimated through DInSAR techniques. In this study, a method is proposed which estimates the atmospheric path delay using a single interferometric pair and an atmospheric path delay estimator. The estimator relies on the minimization of the outage probability, which is the probability that the Mean Square Error (MSE) of the estimated atmospheric component exceeds a desired MSE value. Outage minimization is equivalent to the minimization of the MSE of the atmospheric component for a fixed outage probability. The minimization of the MSE of the atmospheric component is determined by the second-order statistics of the topography and atmospheric components. For a specific SAR image geometry, second-order statistics of the topography component are satisfactorily approximated by the mean squared height errors of a high quality InSAR DEM for various height and slope classes, whereas second-order statistics of the atmospheric component are approximated by the inverse coherence value of the dataset which provides the high quality InSAR DEM. The proposed approach is validated to real satellite images and meteorological measurements.

The coherence matrix from the scattering matrix of a single look polarimetric SAR pixel will have an entropy of zero with the main eigenvalue being equal to the span and the other two eigenvalues being equal to zero. Each scattering matrix element from terrain scatter is a coherent sum from a large number of scatterers in a resolution cell. Entropy/alpha decomposition is only possible where the coherency matrix elements are determined from ensemble covariances. This is the case for multilook polarimetric SAR data where covariances from the exact same collection of scatterers are averaged using separate extraction filters in the SAR doppler direction. We report interesting observations from analysis of multilook SIR-C data at L and C bands from different oceans around the globe. We present a strategy for segmenting single look polarimetric TerraSAR ocean data using an algorithm we have previously developed with the averaging of the resulting like pixels used to generate coherence matrices. We give a brief discussion of desert surfaces.

The U.S. Army Research Laboratory (ARL) recently designed and tested a new prototype radar, the Spectrally Agile Frequency-Incrementing Reconfigurable (SAFIRE) radar system, based on a stepped-frequency architecture to address issues associated with our previous impulse-based radars. This is a low-frequency ultra-wideband (UWB) radar with frequencies spanning from 300 to 2000 MHz. Mounted on a vehicle, the radar can be configured in either sidelooking or forward-looking synthetic aperture radar (SAR) mode. We recently conducted our first experiment at Yuma Proving Grounds (YPG). This paper summarizes the radar configurations, parameters, and SAR geometry. The radar data and other noise sources, to include the self-interference signals and radio-frequency interference (RFI) noise sources, are presented and characterized in both the raw (pre-focus) and SAR imagery domains. This paper also describes our signal processing techniques for extracting noise from radar data, as well as the SAR imaging algorithms for forming SAR imagery in both forward- and side-looking modes. Finally, this paper demonstrates our spectral recovery technique and results for a radar operating in a spectrally restricted environment.

A high speed, high resolution spectrum measurement system based on fiber-spectrometer was built to diagnose the high temperature hypersonic combustion flow. The theoretical models of the spectral radiance and transmittance of the hypersonic combustion flow were established in this paper. The spectral radiance and transmittance of the hypersonic combustion flow were measured at the combustion wind tunnel of BISLMV. Preliminary experiments showed that the spectral radiance behaved not like typical gas radiation but have a continuous spectrum, and the spectral transmittance of the combustion gas flow was about 0.9 in the spectral range 500-900nm without strong spectral selection. The results obtained in this paper will benefit the surface temperature measurement of the thermal protection materials of space vehicle tested at BISLMV.

The atmospheric turbulence has a strong influence on laser transmission in the atmosphere. As a important parameter, atmospheric coherence length measures the atmospheric turbulence and it is very significant to determine the atmospheric conditions. This system puts into use visible wavelength is 532 nm ~ 680 nm , the charge coupled device size is 12.7 mm . The three component mechanically compensating zoom detecting system is designed, it has simple structure, low cost and real-time monitoring.

The space-based information moving target detection method is mainly based on the traditional SAR/GMTI implementation, but at present our country still does not have to orbit satellite SAR/GMTI. This paper presents a minimal time difference with multi spectral image channel method for moving target detection, the multispectral image channel cannot imaging flaws to the clever use, moving object detection and velocity estimation.

Temperature is a critical parameter to diagnose the high temperature hypersonic combustion flow. A fiber-spectrometer based measurement system and the correlated theoretical models to measure the radiation temperature of the “optical thick” hypersonic combustion flow were established in this paper. The spectral responsivity of the fiber-spectrometer based measurement system was measured at NIM in lab condition, and the spectral radiance and emissivity of the hypersonic combustion flow were measured in-situ at the combustion wind tunnel of BISLMV. Preliminary experimental results showed the spectral emissivity of the combustion flow was about 0.1 in the spectral range 500-800nm without strong spectral selection, which resulted in the radiation temperature about 2200 K, with relative standard uncertainty about 10%.

As an important part of the earth, atmosphere plays a vital role in filtering the solar radiation, adjusting the temperature and organizing the water circulation and keeping human survival. The passive atmospheric wind measurement is based on the imaging interferometer technology and Doppler effect of electromagnetic wave. By using the wind imaging interferometer to get four interferograms of airglow emission lines, the atmospheric wind velocity, temperature, pressure and emission rate can be derived. Exploring the multi-functional and integrated innovation of detecting wind temperature, wind velocity and trace gas has become a research focus in the field. In the present paper, the impact factors of the fixed optical path difference(OPD) of near infrared wind imaging interferometer(NIWII) are analyzed and the optimum value of the fixed optical path difference is simulated, yielding the optimal results of the fixed optical path difference is 20 cm in near infrared wave band (the O2(a1Δg) airglow emission at 1.27 microns). This study aims at providing theoretical basis and technical support for the detection of stratosphere near infrared wind field and giving guidance for the design and development of near infrared wind imaging interferometer.

Natural light will be partially polarized or totally polarized after the reflection, scattering, absorption and refraction of the objects. When detecting the ocean from the satellite orbit, the remote sensing signal of water is mainly composed of three parts: radiation signals of atmosphere after photon scattering, the direct reflection of light when the sunlight reaches the surface of the water, and the light after scatting backward. The sunlight will be polarized when it passes the atmosphere. Also, the polarization state of the incident light will be changed when it passes in the water. For remote sensing cameras with quantitative detection application, it is necessary to suppress the polarization sensitivity of the system as far as possible. Through the layout of the optics, the film layer design, the design of the depolarizer, we can achieve low polarization sensitivity.

We focus on condensation process of vapor bubble exposed to a pooled liquid of subcooled conditions. Two different geometries are employed in the present research; one is the evaporation on the heated surface, that is, subcooled pool boiling, and the other the injection of vapor into the subcooled pool. The test fluid is water, and all series of the experiments are conducted under the atmospheric pressure condition. The degree of subcooling is ranged from 10 to 40 K. Through the boiling experiment, unique phenomenon known as microbubble emission boiling (MEB) is introduced; this phenomenon realizes heat flux about 10 times higher than the critical heat flux. Condensation of the vapor bubble is the key phenomenon to supply ambient cold liquid to the heated surface. In order to understand the condensing process in the MEB, we prepare vapor in the vapor generator instead of the evaporation on the heated surface, and inject the vapor to expose the vapor bubble to the subcooled liquid. Special attention is paid to the dynamics of the vapor bubble detected by the high-speed video camera, and on the enhancement of the heat transfer due to the variation of interface area driven by the condensation.

Lidar daylight measurements are limited by sky background noise (BGN). Reducing the BGN is essential to improve Lidar signal-to-noise ratio (SNR). We report on an optimization technique to improve SNR in a monostatic/biaxial and bistatic Lidar systems by redesigning the geometrical scheme of Lidar receiver. A series of simulations to calculate the overlap area between both transmitter and receiver field of view (FOV) is conducted to determine optimal receiver aperture shapes, locations, and sizes within different lidar ranges. Techniques to vary receiver aperture shape, position, and size to accommodate backscattering signals over a given range, to maximize Lidar SNR, is introduced. At the same short range, numerical results show a better GF of the bistatic compared to the monostatic/biaxial configurations. A complete comparison between monostatic/biaxial and bistatic configurations, for low altitude measurements between 0.1km and 2km, is discussed.

© 2017 SPIE. Since wind power has intermittent, irregular and volatility nature, improving load forecasting accuracy of wind power has significant influence on controlling wind system and guarantees stable operation of power grids. This paper constructed the wind farm loading forecasting in short-term based on Elman neural network, and made a numerical example analysis. Examples show that, using input delayed of feedback Elman neural network, can reflect the inherent laws of wind load operation better, so as to present a new idea for short-term load forecasting of wind power.

The sensing laser radiation wavelength is one of the most significant factors conditioning the elastic lidar efficiency. Nevertheless, its role in the process of lidar sensing has not been investigated systematically so far. Therefore, the main purpose of the present work is to develop and perform an initial examination of an approach to solve this problem based on modeling the profile of the lidar return signal (the lidar profile) and evaluating, in a specific way, the corresponding profile of the measurement signal-to-noise ratio (SNR). The measurement fluctuations are considered as mainly due to the Poisson shot noise that is intrinsic to the dark current and the photocurrent induced by the useful signal itself and the atmospheric background. The initial results obtained show for instance that for ground-based lidar facilities the maximum Rayleigh return signal is obtainable at wavelengths about 350nm. The roles are changed when sensing clouds using wavelength from 400nm to 1000-2000nm. Then, the longer wavelengths provide higher return power from clouds, and the effect is magnified in aerosol-loaded (and especially hazy) atmosphere. The results of such investigations are useful when selecting optimal lidar-design characteristics ensuring maximum brightness and contrast of the lidar-acquired images of specific aerosol strata and objects in the atmosphere.

Although the fact that lidars are used more than half a century, so many of the technical and methodological problem of the laser sensing has not been resolved. Laser sensing of optically dense aerosol formations (such as clouds or fog) belongs to the need of careful study. This is because the lidar signal from such formations is due not only single, but also multiple scattering, which significantly affects both the intensity value and the state of polarization of the received radiation. We have obtained an analytical expression for the time delay of the lidar return from the cloud layer due to multiple scattering. It is shown that the value of this lidar return is determined by the lower boundary, the microstructure and the thickness of the cloud layer, and a field-of-view of lidar receiving system.

Understanding the impact of gaseous pollutants on the earth's atmosphere, as well as more and more felt by mankind negative effects of its contamination, result in increasing the level of environmental awareness and contribute to the intensification of actions aimed at reducing the emission of harmful gases into the atmosphere. At the same time, the extensive studies are conducted in order to continuously monitor the level of air contamination with harmful gases and the industry compliance with the standards limited the amount of emitted pollutants. Over recent years, there has been increasing use of cascade lasers and multi-pass cells in optical systems detecting the gaseous atmospheric pollutants and measuring the gas concentrations. The paper presents the use of a tunable quantum cascade laser as a source of the IR radiation in an advanced detection system enabling the trace gaseous atmospheric pollutants to be identified. Apart from the laser, the main elements of the system are: a multi-pass cell, an IR detector and a module for control and analysis. Operation of the system is exemplified by measuring the level of the air pollution with ammonia, carbon oxide and nitrous oxide.

Lidar is short for light detection and ranging, which is a tool to help measuring some useful information of atmosphere. In the recent years, more and more attention was paid to the research of wind measurement by lidar. Because the accurate wind information can be used not only in weather report, but also the safety guarantee of the airplanes. In this paper, a more detailed signal model of wind measurement lidar is proposed. It includes the laser transmitting part which describes the broadening of the spectral, the laser attenuation in the atmosphere, the backscattering signal and the detected signal. A Voigt profile is used to describe the broadening of the transmitting laser spectral, which is the most common situation that is the convolution of different broadening line shapes. The laser attenuation includes scattering and absorption. We use a Rayleigh scattering model and partially-Correlated quadratic-Velocity-Dependent Hard-Collision (pCqSDHC) model to describe the molecule scattering and absorption. When calculate the particles scattering and absorption, the Gaussian particles model is used to describe the shape of particles. Because of the Doppler Effect occurred between the laser and atmosphere, the wind velocity can be calculated by the backscattering signal. Then, a two parameter Weibull distribution is used to describe the wind filed, so that we can use it to do the future work. After all the description, the signal model of coherent wind measurement lidar is decided. And some of the simulation is given by MATLAB. This signal model can describe the system more accurate and more detailed, so that the following work will be easier and more efficient.

In order to ensure the radiometric imaging quality for the space-borne camera with super-wide field of view, we put forward a new method, with which the apparent spectral radiance for any field of view can be precisely calculated. Firstly, building the imaging model for the space-borne camera, and the parameters of the orbits and attitudes of satellite, the look direction for the given field of view, the characteristics of different ground objects, the state of the atmosphere, et al.. Secondly, calculating the geometrical observation parameters for the given look direction of the space-borne camera. Finally, using the radiative transfer model to calculate the value of the apparent spectral radiance. Then, we use this method to calculate the apparent spectral radiance for the space-borne camera with the FOV of 75°based on freeform mirror on a small remote sensing satellite. And the result shows that the relative non-consistency of the apparent spectral radiance can be 25.3%, when the satellite takes the imaging of the area of North Atlantic. And we should greatly consider the characteristic of the radiometric imaging quality for the space-borne camera with super-wide field of view.

The water vapor noise will affect the accuracy of the extracted optical parameters based on terahertz time domain spectroscopy technology. Because vapor noise has the characteristics of wide distribution and high intensity, the existing denoising methods cannot be effectively applied to the THz signal with vapor noise. In this paper, a numerical denoising method is presented. First, based on Van Vleck-Weisskopf lineshape function and the linear absorption spectrum of water molecules in the HITRAN database, we have simulated the water vapor absorption spectrum with line width, and the continuum effect of water vapor molecules are considered in the simulation. Then, the transfer function of different humidity is constructed by the calculation of the water vapor absorption coefficient and the real refractive index; Finally, based on the propagation factor formula of the mutual effects of THz wave and water vapor, the THz signal of the Lacidipine sample containing vapor noise in the continuous frequency domain of 0.3-1.8THz is denoised by using the constructed transfer function of the water vapor; the optical parameters of the sample signal before and after denoising can be extracted. It can be seen that the optical parameters extracted from the denoised signal are close to the optical parameters in the nitrogen environment, which proves the effectiveness of denoising. Under low humidity, this method can still accurately extract the optical parameters of samples without nitrogen filling, which saves the cost, enhances the convenience of the application of terahertz time domain spectroscopy in pharmaceutical production, safety inspection, imaging etc.

The millimeter-wave cloud radar can provide a large number of fine and reliable information for the inversion of cloud macro and micro parameters. A key link of using the millimeter-wave cloud radar to detect the cloud is that the radar must be calibrated. Due to the precision components and severe environment of millimeter-wave cloud radar, subtle changes may take place in the operation process of cloud radar, unless the cloud radar is calibrated regularly. Although the calibration system inside the cloud radar can track and monitor the main working parameters and correct the detection results, it fails to consider the characteristics of the antenna and the mutual influence among different components of cloud radar. Therefore, the external calibration for cloud radar system is very important. Combined with the actual situation of cloud radar under domestic onboard platform, this paper builds a complete external calibration technique process of cloud radar based on the calm sea, providing the theoretical support for the external calibration experiments of the airborne and even satellite-borne millimeter-wave cloud radar developed by our country.

Aerosol light absorption plays an important role in the earth’s atmosphere direct and semi-direct radiate forcing, simultaneously, it also has a huge influence on the visibility impairment and laser engineering application. Although various methods have been developed for measuring aerosol light absorption, huge challenge still remains in precision, accuracy and temporal resolution. The main reason is that, as a part of aerosol light extinction, aerosol light absorption always generates synchronously with aerosol light scattering, and unfortunately aerosol light scattering is much stronger in most cases. Here, a novel photo-thermal interferometry is proposed only for aerosol absorption measurement without disturbance from aerosol scattering. The photo-thermal interferometry consists of a sinusoidal phase-modulating single mode fiber-optic interferometer. The thermal dissipation, caused by aerosol energy from photo-thermal conversion when irritated by pump laser through interferometer, is detected. This approach is completely insensitive to aerosol scattering, and the single mode fiber-optic interferometer is compact, low-cost and insensitive to the polarization shading. The theory of this technique is illustrated, followed by the basic structure of the sinusoidal phase-modulating fiber-optic interferometer and demodulation algorithms. Qualitative and quantitative analysis results show that the new photo-thermal interference is a potential approach for aerosol absorption detection and environmental pollution detection.

Exhaust plume flow field have the characteristics of high temperature, high speed and multi-species flow. Exhaust plume infrared signal are important basis of diagnosing, detecting and identifying plume spectrum. This paper focuses on the infrared radiation characteristics of high-altitude plume. The plume flows exhausted from a micro-nozzle of a low-thrust engine at high-altitude have been simulated numerically through using a DSMC method. Both the properties of plume flow at high altitude and the non-equilibrium effect related to rarefied gases are analyzed. Results are given numerically in good agreement with high-altitude plume observations. With the fields of pressure, temperature and main components of the exhaust plume as input data, the line-by line method was used to calculate the 2~5μm infrared spectral radiation properties of the plume. Different flight conditions are considered to analyze the influence on the infrared radiation characteristics. Some interesting conclusion are finally achieved.

Form of sea wave is greatly affected by not just flow and depth of sea water, but also wind blowing on the sea surface. Therefore, measurement and analysis of sea wave motion is of assistance for control and operational safety of boats and ships. Generally, oceanic information is gauged by acoustic and electric wave. But these methods have not provided enough spatial and temporal resolution, and are completely out of touch with the on-site needs. Thus, the LED liar for sea wave measurement has been developed. The dynamic analysis of sea wave image measured by the LED lidar was conducted and the relationship with wind speed was evaluated. In this report, we first present the specifications and measurement methodologies of the LED lidar. Then we describe the actual measurements of sea wave with shallow angle by using this lidar and the results of their analysis.

Joint analysis of the data on polarization laser sensing of cirrus obtained using the ground based polarization laser developed at National Research Tomsk State University (Russia, Tomsk) with the results of theoretical calculations is described. The possibility of estimation of the microstructure parameters of cirrus with a preferred orientation of ice crystals on the basis of comparison of the backscattering phase matrices obtained experimentally and calculated theoretically is discussed.

Space-borne coherent wind lidar technique is considered as one of the most promising and appropriate remote Sensing methods for successfully measuring the whole global vector wind profile between the lower atmosphere and the middle atmosphere. Compared with other traditional methods, the space-borne coherent wind lidar has some advantages, such as, the all-day operation; many lidar systems can be integrated into the same satellite because of the light-weight and the small size, eye-safe wavelength, and being insensitive to the background light. Therefore, this coherent lidar could be widely applied into the earth climate research, disaster monitoring, numerical weather forecast, environment protection. In this paper, the 2μm space-borne coherent wind lidar system for measuring the vector wind profile is proposed. And the technical parameters about the sub-system of the coherent wind lidar are simulated and the all sub-system schemes are proposed. For sake of validating the technical parameters of the space-borne coherent wind lidar system and the optical off-axis telescope, the weak laser signal detection technique, etc. The proto-type coherent wind lidar is produced and the experiments for checking the performance of this proto-type coherent wind lidar are finished with the hard-target and the soft target, and the horizontal wind and the vertical wind profile are measured and calibrated, respectively. For this proto-type coherent wind lidar, the wavelength is 1.54μm, the pulse energy 80μJ, the pulse width 300ns, the diameter of the off-axis telescope 120mm, the single wedge for cone scanning with the 40°angle, and the two dualbalanced InGaAs detector modules are used. The experiment results are well consisted with the simulation process, and these results show that the wind profile between the vertical altitude 4km can be measured, the accuracy of the wind velocity and the wind direction are better than 1m/s and ±10°, respectively.

Remote sensing using THz wave has irreplaceable advantage comparing to the microwave and the infrared waves, and study on the THz remote sensing become more and more popular in recent years. The major applications of the remote sensing in THz wavelengths are the retrieval of the atmospheric parameters and the microphysical information of the ice cloud. The remote sensing of the atmosphere is based on the radiation of THz wave along the earth-space path of which the most significant part is the upward radiation of the atmosphere. The upward radiation of the atmosphere in sunny day in the low latitude area is computed and analyzed in this paper. The absorption of THz wave by the atmosphere is calculated using the formulations illustrated in the Recommendation ITU-R P.676 to save machine hour, the frequency range is then restricted below 1THz. The frequencies used for the retrieval of atmospheric parameters such as temperature and water content are usually a few hundred GHz, at the lower end of THz wavelengths, so this frequency range is sufficient. The radiation contribution of every atmospheric layer for typical frequencies such as absorption window frequencies and peak frequencies are analyzed. Results show that at frequencies which absorption is severe, information about lower atmosphere cannot reach the receiver onboard a satellite or other high platforms due to the strong absorption along the path.

For the satellite remote sensing data, it is necessary to evaluate the adjacency effect due to atmospheric scattering. Accurate modeling of the adjacency effect requires capabilities dealing with rugged areas and multiple scattering. In this paper, estimation of the adjacency effect is done by calculating the contribution of photons after the multiple scattering process through a many layered atmosphere. For the requirement of fast calculation in remote sensing simulation system, we adopt the approximate ISAACS 2-stream and flux adding method to model the adjacency effect. We evaluate the multiple scattering model by simulating the at-sensor radiance observed over synthetic rugged scenes under varying atmospheric conditions. Radiance comparisons with a single scattering model show good agreement in the clear atmosphere. Relative radiance differences are found to be about 11% in the dust atmosphere, increasing to 15% in the steep areas. Being coupled with the simulation model for remote sensing, it can be used in generation of simulated datasets and validation of the data processing algorithms.

This paper evaluates the rain effects on Ku-band radar backscatter at low incidence angles. The data used consisted of the sea surface backscatter and averaged rain rates from Tropical Rainfall Mapping Mission precipitation radar (TRMM PR) measurements and the collocated 10-m height numerical prediction wind speeds from the European Centre for Medium-Range Weather Forecasts (ECMWF). The wind-induced backscatter was estimated by the Ku-band low incidence backscatter model (KuLMOD) and possible bias due to different wind speed inputs was considered. The rain effect was analysed by comparing the TRMM PR-measured surface backscatter for the rain-affected sea surface with the collocated wind-induced backscatter. We found that the surface backscatter decreases with increases in the averaged rain rate. The rain-induced backscatter was clearly dependent of the wind speed and was slightly dependent of the incidence angle. Results show that it is necessary to develop a wind and rain backscatter model instead of single wind backscatter model.

Earth’s atmosphere can significantly impact the propagation of electromagnetic radiation, degrading the performance of imaging systems. Deleterious effects of the atmosphere include turbulence, absorption and scattering by particulates. Turbulence leads to blurring, while absorption attenuates the energy that reaches imaging sensors. The optical properties of aerosols and clouds also impact radiation propagation via scattering, resulting in decorrelation from unscattered light. Models have been proposed for calculating a point spread function (PSF) for aerosol scattering, providing a method for simulating the contrast and spatial detail expected when imaging through atmospheres with significant aerosol optical depth. However, these synthetic images and their predicating theory would benefit from comparison with measurements in a controlled environment. Recently, Michigan Technological University (MTU) has designed a novel laboratory cloud chamber. This multiphase, turbulent “Pi Chamber” is capable of pressures down to 100 hPa and temperatures from -55 to +55°C. Additionally, humidity and aerosol concentrations are controllable. These boundary conditions can be combined to form and sustain clouds in an instrumented laboratory setting for measuring the impact of clouds on radiation propagation. This paper describes an experiment to generate mixing and expansion clouds in supersaturated conditions with salt aerosols, and an example of measured imagery viewed through the generated cloud is shown. Aerosol and cloud droplet distributions measured during the experiment are used to predict scattering PSF and MTF curves, and a methodology for validating existing theory is detailed. Measured atmospheric inputs will be used to simulate aerosol-induced image degradation for comparison with measured imagery taken through actual cloud conditions. The aerosol MTF will be experimentally calculated and compared to theoretical expressions. The key result of this study is the proposal of a closure experiment for verification of theoretical aerosol effects using actual clouds in a controlled laboratory setting.

The electromagnetic (EM) scattering features of radar scattered echoes from nearshore sea surfaces are investigated using the second-order small-slope approximation (SSA-II). The joint influences of wind fetch and water depth on the normalized radar cross section (NRCS) of and Doppler spectra for echoes from nearshore sea surfaces are mainly studied. The numerical results show that with a further increasing fetch, the excess of NRCS for small depth sea over that for deeper sea increases, and Doppler spectral features are also intensely influenced by nonlinear interactions between waves in the large wind fetch and small water depth marine environment. These both indicate that the effects of the finite depth are more prominent with increasing wind fetch, especially for HH polarization.

Preliminary measurements of profiles of aerosol/cloud in the lower atmosphere using a homemade stationary groundbased lidar system will be presented. In addition, information on basic characteristics and performance of the lidar system will be provided. Aerosol/Cloud lidar system in monostatic coaxial configuration uses the fundamental (1064 nm) and the second harmonic (532 nm) of a pulsed solid state Nd:YAG laser to provide information on the relative concentration and spatial distribution of aerosol particles and cloud water droplets. Beam expander is used to reduce the laser beam divergence before to be transmitted into the atmosphere. In this study, high-resolution vertical profiles from the near ground up to 15 km altitude are obtained. A Newtonian telescope of diameter 400 mm with an adjustable field of view (FOV) is used to collect the elastic backscattered signal. A photomultiplier tube (PMT) is used for the 532 nm wavelength detection channel, while an avalanche photodiode (APD) is used for the 1064 nm wavelength detection channel. The optoelectronic detection channels use two similar very high frequency preamplification circuit. Data are acquired with a nominal spatial resolution of 7.5 m using a 12-bit 20 MHz analog-to-digital converter (ADC) for each channel. Many functions, such as, range determination, background subtraction, digitization, and averaging are performed by the receiver subsystem. In addition, spatial resolution and linear dynamic range were optimized during signal processing.

Optical properties of the cirrus cloud ice crystals with preferred azimuthal orientation are required for current numerical models of the Earth's radiation balance. Retrieving the orientation distributions function of the crystals from a vertically pointing polarization lidar measuring the full Mueller matrix is a very complicated problem because of lake of information. Lidars with zenith scanning can be used only to retrieve the properties of horizontally oriented particles. The paper shows that if the particles have preferred azimuthal orientation, the polarization lidars with azimuthal scanning should be used. It is also shown that all the elements of the Mueller matrix give no extra information compare to the depolarization ratio. Optical properties of preferred azimuthal oriented hexagonal ice columns with size from 10 to 1000 μm for wavelengths of 0.355, 0.532 and 1.064 μm were collected as a data bank.

Investigation of the Doppler shift of radar return from the sea surface is very important for better understanding of capabilities of exploitation of microwave radar for measuring velocities of marine currents. Here new field experiments carried out from a Platform on the Black Sea with a coherent X-band scatterometer, and a Doppler multifrequency (X- /C-/S-band) dual-polarized radar recently designed at IAP RAS are discussed. It is shown that the radar return contains both Bragg (polarized) and non polarized scattering components, presumably giving different contributions to radar Doppler shifts. Radar Doppler shifts were estimated using two different definitions as a) a frequency of the “centre of gravity” of an instantaneous radar return spectrum (ASIS) averaged over periods of dominant wind waves and b) the “centre of gravity” of the averaged over dominant wave periods spectrum (SAS). The ASIS and SAS values for both VV and HH-polarizations are shown to be different due to effects of radar backscatter modulation by dominant (long) wind waves. The radar Modulation Transfer Function (MTF) has been analyzed from experimental data and difference between SAS- and ASIS-values has been satisfactory explained using the measured MTF-values. It is obtained that experimental values of ASIS can be satisfactory described by the Bragg model despite the significant contribution of NP component to the radar backscatter. A physical explanation of the effect is given.

Physical properties, such as density, refractive index and morphology of the aerosol particles will be changed when the relative humidity of the environment is relatively high, which leads to a significant variation of the scattered light signal collected by the single particle light scattering measurement system. If the calibration parameters in the condition of low humidity are applied to inverse aerosol mass concentration, the measurement accuracy will certainly be degraded. Therefore, the calibration parameters of the system must be corrected. In this case, the monotonic relationship between the particle size and the scattered light signal collected by the system should be considered carefully. Combining the Mie scattering theory with the humidity growth model of the particle size and the refractive index, the influence of relative humidity on the scattered light signals of spherical particles has been investigated in this paper. The results indicate that the diameters of spherical particles grow exponentially and the refractive index decreases linearly when the relative humidity is increased between 60% and 95%. Consequently, a significant change of the angular distribution of the scattering intensity occurs. The forward-scattered light is getting stronger, while the back-scattered light becomes weaker. Meanwhile, the scattered light flux of the particle within a solid angle displays exponential growth with increasing the relative humidity. Thus, the monotonous relationship between the particle size and the scattered light flux has changed significantly in the case of the high humidity, and their quadratic coefficient decreases clearly assuming the particle density invariant, which causes an obvious increase of the calibrated proportional coefficient. The results of this work provide an important theoretical guidance for the humidity correction of calibration parameters for the inversion of aerosol mass concentration by the single particle light scattering method.

We present a physics-based model for analysis of atmospheric turbulence and aerosol scattering effects on imaging of remote extended objects under daylight and laser illumination. The technique is based on joint solution of the parabolic wave equation and equation for the brightness function. Turbulent distortions are simulated with the use of the conventional phase-screen approach. Scattering effects are accounted for by representing the aerosol medium by a set of aerosol screens. The coherent and incoherent components of the scattered field are obtained in the single scattering approximation at each aerosol screen. In addition, a simplified model considering the natural background radiation effect on the contrast of an image formed is discussed. Numerical simulation results are presented.

The Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite is a passive scanning radiometer and an imager, observing radiative energy from the Earth in 22 spectral bands from 0.41 to 12 m which include 14 reflective solar bands (RSBs). Extending the formula used by the Moderate Resolution Imaging Spectroradiometer instruments, currently the VIIRS determines the sensor aperture spectral radiance through a quadratic polynomial of its detector digital count. It has been known that for the RSBs the quadratic polynomial is not adequate in the design specified spectral radiance region and using a quadratic polynomial could drastically increase the errors in the polynomial coefficients, leading to possible large errors in the determined aperture spectral radiance. In addition, it is very desirable to be able to extend the radiance calculation formula to correctly retrieve the aperture spectral radiance with the level beyond the design specified range. In order to more accurately determine the aperture spectral radiance from the observed digital count, we examine a few polynomials of the detector digital count to calculate the sensor aperture spectral radiance.

A diode laser sensor based on absorption spectroscopy has been developed for the measurement of spectroscopic parameters of the R(50) line at 5007.787cm-1 (20012

The ultimate objective of this work is to improve characterization of the ice cover distribution in the polar areas, to improve sea ice mapping and to develop a new automated real-time high spatial resolution multi-sensor ice extent and ice edge product for use in operational applications. Despite a large number of currently available automated satellite-based sea ice extent datasets, analysts at the National Ice Center tend to rely on original satellite imagery (provided by satellite optical, passive microwave and active microwave sensors) mainly because the automated products derived from satellite optical data have gaps in the area coverage due to clouds and darkness, passive microwave products have poor spatial resolution, automated ice identifications based on radar data are not quite reliable due to a considerable difficulty in discriminating between the ice cover and rough ice-free ocean surface due to winds. We have developed a multisensor algorithm that first extracts maximum information on the sea ice cover from imaging instruments VIIRS and MODIS, including regions covered by thin, semitransparent clouds, then supplements the output by the microwave measurements and finally aggregates the results into a cloud gap free daily product. This ability to identify ice cover underneath thin clouds, which is usually masked out by traditional cloud detection algorithms, allows for expansion of the effective coverage of the sea ice maps and thus more accurate and detailed delineation of the ice edge. We have also developed a web-based monitoring system that allows comparison of our daily ice extent product with the several other independent operational daily products.

Effective hyperspectral thermal infrared imaging requires accurate atmospheric compensation to convert the measured at-sensor radiance to the ground radiance. The ground radiance consists of the thermal emission of the material and the reflected downwelling radiance. An accurate estimate of the downwelling radiance is required for temperature-emissivity separation (TES) to remove the spectrally sharp reflected atmospheric effects and retrieve a smooth and accurate material emissivity to use for detection. Determination of the downwelling radiance is difficult due to the fact that a down-looking sensor has no knowledge of the atmospheric properties above its line of sight. As the sensor altitude increases and more of the atmospheric emitters are below the sensor, a relationship forms between the upwelling and downwelling radiances. This relationship comes at the expense of increased pixel size, which increases the likelihood of mixed pixels and nonlinear spectral mixing. In this paper improvements to methods used to estimate the downwelling radiance of low altitude collections are proposed. The ground radiances of reflective pixels are used to estimate the atmosphere above the sensor. The reflective pixels are identified from their sharp atmospheric spectral features. Using the assumption that emissivity spectra are smooth across the narrow reflected atmospheric downwelling radiance features, the temperatures and emissivities are then separated for the reflective pixels using a look-up-table of downwelling radiances. The downwelling radiance that provides the best overall fit for the reflective pixels is then chosen as the scene downwelling radiance.

A compact light detection and ranging (LiDAR) system provides aerosols profile measurements by identifying the aerosol scattering ratio as function of the altitude. The aerosol scattering ratios are used to obtain multiple aerosol intensive ratio parameters known as backscatter color ratio, depolarization ratio and lidar ratio. The aerosol ratio parameters are known to vary with aerosol type, size, and shape. Different methods in the literature are employed for detection and classification of aerosol from the measurements. In this paper, a comprehensive review for aerosol detection methods is presented. In addition, results of implemented methods of quantifying aerosols in the atmosphere on real data are compared and presented showing how the backscatter color, depolarization and lidar ratios vary with presence of aerosols in the atmosphere.

In the haze and other weather conditions, the scattering of atmospheric particles leads to a serious degradation of the captured images. In this paper, we present a new fast defogging method based on physical model. The algorithm is based on the atmospheric scattering model to simplify the atmospheric scattering model by using the white balance. A fast bilateral filtering method is used to estimate the atmospheric veil, and then recover the visibility. The time complexity of the algorithm is linear function of the number of image pixels, which has a very fast execution speed. Experimental results show that the proposed algorithm can effectively restore the contrast and color of the scene, so that the image can be improved significantly.

The resolution of a conventional optical imaging radar system is constrained by the diffraction limit of the telescope’s aperture. The combination of the lidar and synthetic aperture processing techniques can overcome the diffraction limit and provide a higher resolution air borne remote sensor. Atmospheric turbulence is an important factor affecting the lidar imaging, and phase screen simulation method is an effective method to simulate the degradation of laser signal propagating in turbulent atmosphere. This paper proposes a kind of phase screen generation method based on Monte-Carlo random factor. The expansion of phase data units can be selected by Monte-Carlo random factor which can increase the randomness of phase screens. The radar imaging with different turbulence intensity is also calculated in this paper, then the improved rank one phase estimation autofocus method is used to compensate the imaging phase errors. The results show that the method of generating phase screen is consistent with the statistics of atmospheric turbulence, which can well simulate the effect of atmospheric turbulence on synthetic aperture lidar, and the influence on synthetic aperture lidar azimuth resolution is greater when atmospheric turbulence is stronger. Improved rank one phase estimation algorithm has good autofocus effect, which can effectively compensate the phase errors and enhance the image quality degraded by turbulence.

The formation of water ice on key thermal and optical surfaces is a factor in the design of the James Webb Space Telescope. Many of these concerns are related to the mid-infrared stray light performance of the system. In this paper, an expression for the radiance of a contaminated surface is formulated, including directional, film thickness and cooling effects. The resulting formula is then evaluated to show how radiance emanating from the surface changes for various thicknesses of the ice layer as a function wavelength and the local thermal environment. This paper concludes with an analysis and discussion of this complex behavior.

ASTRI SST-2M is an end-to-end telescope prototype developed by the Italian National Institute of Astrophysics (INAF) in the framework of the Cherenkov Telescope Array (CTA). The CTA observatory, with a combination of large-, medium-, and small-sized telescopes (LST, MST and SST, respectively), will represent the next generation of imaging atmospheric Cherenkov telescopes. It will explore the very high-energy domain from a few tens of GeV up to few hundreds of TeV. The ASTRI SST-2M telescope structure and mirrors have been installed at the INAF observing station at Serra La Nave, on Mt. Etna (Sicily, Italy) in September 2014. Its performance verification phase began in autumn 2015. Part of the scheduled activities foresees the study and characterization of the optical and opto-mechanical performance of the telescope prototype. In this contribution we report the results achieved in terms of kinematic model analysis, mirrors reflectivity evolution, telescopes positioning, flexures and pointing model and the thermal behavior.

The Southern African Large Telescope (SALT) is a 10-m class 91-segment fixed altitude telescope located at Sutherland, South Africa. The segment alignment is maintained by inductively coupled sensors mounted on Sitall brackets beneath the segments. An extensive period of testing in environmental chambers and on the telescope has been conducted to establish the stability of the sensors and their response to temperature and humidity variations in the telescope chamber. We present some of the test results, including a demonstration of the ability of the sensors to maintain the alignment of the primary mirror over a period of 6 days.

In 2013 the process of developing an Orbital Debris and Satellite observation capability for the United Kingdom Infrared Telescope was initiated. This process involved the modification of various operational aspects of the observatory. After a year of implementing the modifications the observatory was capable of providing deep space observations of orbital debris and satellites in a queue based format. The telescope has been operating with this capability for the past 2.5 years and has generated terabytes of observational data on orbital debris and satellites that are in the GEO satellite belt distributed across the Pacific Ocean.