Search

The Moon is a very useful calibration target for Earth-observing sensors in orbit because its surface is radiometrically stable and it has a radiant flux comparable to Earth scenes. To predict the lunar irradiance given an illumination and viewing geometry, the United States Geological Survey (USGS) has developed the Robotic Lunar Observatory (ROLO) Model of exo-atmospheric lunar spectral irradiance. The USGS ROLO model represents the current most precise knowledge of lunar spectral irradiance and is used frequently as a relative calibration standard by space-borne Earth-observing sensors. However, its accuracy as an absolute reference may be limited to several percent and it is not SI-traceable. Advancing the model to be a more accurate absolute lunar reference requires new measurements. The objective of the airborne LUnar Spectral Irradiance (Air-LUSI) mission is to make highly accurate, SI-traceable measurements of lunar spectral irradiance in the VNIR spectral region from NASA’s high-altitude ER-2 aircraft, above 95% of the atmosphere. To that end, the Air-LUSI system uses a non-imaging telescope system that robotically tracks the Moon in flight, fiber-optic coupled to a stable spectrometer housed in an enclosure providing a robustly controlled environment. The spectrometer measures about 350 to 1050 nm at 3.8 nm resolution, with 0.8 nm sampling. The instrument is reproducibly stable to 0.3% and rigorously calibrated before and after campaigns and flights using a similar transfer standard spectrograph. An on-board LED source is used to monitor the instrument response during flight ascent and descent. Air-LUSI successfully conducted a Demonstration Flight Campaign on five consecutive nights from 12 to 17 November 2019, corresponding to lunar phase angles of about 10°, 21°, 34°, 46° and 59°. Each night, the Air-LUSI system observed the Moon from above 68,000 feet altitude for 30 to 40 minutes. To reach a target uncertainty for lunar irradiance of 0.5% (k=1), processing the raw data to exo-atmospheric lunar spectral irradiance required accounting for various known behaviors of the instrument, such as thermal and stray light corrections. Additional measures were taken to address variances idiosyncratic to the campaign and were factored into the measurement error budget. The resulting error budget currently stands at less than 1% over most of the VNIR range. This paper reviews the steps taken towards high accuracy results for Demonstration Flight Campaign, how they factored in the error budget, and how our uncertainty target can be met in future campaigns.

Current uncertainty requirements for the measurement of global variables relevant to climate change modeling in the reflected solar range are 0.5 % to 1 % for solar and lunar spectral irradiance and 0.5 % to 2 % for Earth reflected radiance. Future uncertainty requirements, as defined by CLARREO mission requirements, include laboratory calibration uncertainties are 0.2 % over the 500 nm to 900 nm spectral range and 1 % or less over the rest of the spectral region from 320 nm to 2300 nm. The uncertainties in lamp-illuminated integrating spheres, a principal calibration artifact, ranging from 2% to 3 % in the visible to near-infrared and 3 % to 5 % in the short-wave infrared, do not meet either current or future uncertainty requirements. NIST uncertainties in broad-band lamp-based calibration artifacts are traceable to primary standard blackbodies. The irradiance and radiance responsivity scales disseminated by the NIST laser-based SIRCUS calibration facility are held by primary standard irradiance meters traceable to the Primary Optical Watt Radiometer and dimensional metrology from the NIST Aperture Area Facility. The SIRCUS facility has demonstrated that moving from source-based scales traceable to primary standard blackbodies to detector-based scales offer opportunities to reduce the uncertainties in disseminated standards. This presentation discusses existing primary radiometric standards and the uncertainties in detector-based radiance and irradiance scales, validation of their uncertainty budgets through measurements of primary standard metal melting point blackbodies, development of low temperature active cavity radiometers operating in irradiance mode, and the development of transfer standard spectrographs. Finally, this paper discusses possible further developments at NIST aimed at supporting future climate benchmark instrument uncertainty requirements.

In December 2014, NIST’s laser-based Traveling SIRCUS calibration system was installed at Raytheon SAS in El Segundo, CA for testing of the NOAA/NASA Joint Polar Satellite System-1 (JPSS-1) VIIRS sensor’s visible and near-infrared bands. The tunable laser sources were installed in the ante-room outside the Raytheon clean room where the VIIRS sensor was located. The output from the tunable lasers was fiber-coupled into a 1-m diameter Spectralon integrating sphere source positioned in front of the VIIRS sensor’s Earth-view port and VIIRS Absolute Spectral Responsivity (ASR) measurements were made. In a second configuration, a polarizer was placed between the source and the VIIRS entrance port and polarization sensitivity testing was done. In this work, we present details of the T-SIRCUS calibration system, including a new automated tunable Optical Parametric Oscillator (OPO) system, achievable radiances with the 1-m Spectralon integrating sphere, and an uncertainty budget for the integrating sphere radiance. An approach to extend the dynamic range of out-of-band measurements using a recently develop Flat Plate Illuminator will be introduced. Finally, VIIRS sensor ASR and polarization responsivity results and implications based on the measurements are discussed.

During NASA’s Earth Observing System-era, a series of source radiance validation campaigns were planned and executed by the EOS Project Office with the goal of validating the radiances assigned to laboratory calibration sources, principally lamp-illuminated integrating spheres, and establishing uncertainty budgets for the disseminated radiance scale. Based on an analysis of 7 years’ worth of data, Butler et al.1 assigned an uncertainty in disseminated radiance scales of 2% to 3% in the Vis/NIR (silicon) region, increasing to 5% in the short-wave infrared region. The uncertainty in the radiance scale met EOS requirements. For example, the radiance uncertainty requirement for MODIS was 5% in the Vis/NIR spectral region and the uncertainty in disseminated radiance scales met or exceeded sensor calibration requirements. Looking to the future, uncertainty requirements for radiance are reduced below 1% [2]. Uncertainties in the radiance scale in disseminated sources from NIST cannot be reduced and alternate approaches need to be considered to meet future satellite sensor uncertainty requirements. In this presentation, the radiometric characterization and calibration of a spectrograph along with its uncertainty budget are discussed. Its long-term stability is presented and its potential use as a transfer standard radiometer is discussed. The combined standard uncertainty in the spectrograph responsivity is estimated to be 0.25% (k=1), representing a potential order of magnitude reduction in the uncertainty in the radiance of laboratory calibration sources. [1] Butler, J. J., et al., Validation of radiometric standards for the laboratory calibration of reflected-solar Earth observing satellite instruments, Proc. SPIE 6677, 667707 (2007). [2] Ohring, G., et al. (eds.), Satellite Instrument Calibration for Measuring Global Climate Change, NISTIR 7047 (2004).

Laser-based laboratory calibrations in the facility for Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources (SIRCUS) of the National Institute of Standards and Technology (NIST) have achieved detector calibration with uncertainties less than 0.1 % in the silicon spectral region. Because of the high power of lasers, there is also a drastic increase in dynamic range covering more than 5 orders of magnitude. The low measurement uncertainty and high dynamic range allow accurate assessment of out-of-band performance for flight instruments such as the Suomi National Polar-orbiting Partnership (NPP) Visible and Infrared Imager Radiometer Suite (VIIRS) sensor which was calibrated in 2010 for Absolute Spectral Responsivity (ASR) with full aperture illumination using a tunable laser and a large integrating sphere with an approximately 0.5% uncertainty in radiance responsivity. With the calibration data, it is now possible to fully evaluate the effect of out-of-band (OOB) contribution on at-sensor water-leaving radiance and derive strategy to alleviate variations from OOB scattering and reduce data product uncertainties. In this work, we present a sensitivity analysis of the Top-of-Atmosphere (TOA) measurement for varying chlorophyll concentrations and column water vapor based on measured detector Relative Spectral Responsivity (RSR). A conventional band-averaged radiance approach is taken and histograms are presented for different bands of radiometers to illustrate the data uncertainty from these variations as well as the global seasonal differences. We show how conventional lamp calibration at ground and on board solar calibration resulted in large deviation from OOB scattering because of mismatch with ocean color spectra. We will also present similar analysis for the detectors of the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS).

Mobile information technology can help first responders assist patients more quickly, reliably, and safely, while focusing resources on those most in need. Yet the disaster setting complicates reliable networked computing. The WIISARD client-server architecture provides mobile IT support for medical response in disasters. Cached remote objects (CROs) are shared via publish/subscribe, enabling disconnected operation when out of network range and ensuring data consistency across clients with rollback/replay. CROs also provide a flexible, familiar, and performant programming model for client programmers. A drill with the San Diego MMST showed that a basic client-server architecture, even with CRO's, is insufficient, because prolonged network failures-to be expected in disaster reponse-inhibit group work. We describe an extension of the CRO model to clusters of computers that supports group work during network failures.

The Marine Optical System (MOS) is a dual charge-coupled device (CCD)-based spectrograph system developed for in-water measurements of downwelling solar irradiance Ed and upwelling radiance Lu. These measurements are currently used in the calibration and validation of satellite ocean color measurement instruments such as the moderate resolution imaging spectroradiometer (MODIS) and the Sea-viewing Wide Field-of view Sensor (SeaWiFS). MOS was designed to be deployed from a ship for single measurements and also integrated into the Marine Optical Buoy (MOBY) for longer time series datasets. Measurements with the two spectrographs in the MOS systems can be compared in the spectral interval from about 580 to 630 nm. In this spectral range, they give different values for Lu or Ed at a common wavelength. To better understand the origin of this observation and the sources of uncertainty in the calibration of MOBY, an MOS bench unit was developed for detailed radiometric characterization and calibration measurements in a laboratory setting. In the work reported here, a novel calibration approach is described that uses a tunable laser-based, monochromatic, spatially uniform. Lambertian, large area integrating sphere source (ISS). Results are compared with those obtained by a conventional approach using a lamp-illuminated ISS. Differences in the MOS bench unit responsivity between the two calibration approaches were observed and attributed to stray light. A simple correction algorithm was developed for the lamp-illuminated ISS that greatly improves the agreement between the two techniques. Implications for water-leaving radiance measurements by MOS are discussed.

The traditional university campus is designed to foster a thriving community of learners, but modernity has introduced many stresses. Mobile computing holds the potential to strengthen a campus's traditional institutions of community by creating serendipitous learning opportunities through a process of indirect mediation. This paper introduces ActiveCampus, a suite of personal services for sustaining an educational community based on this idea.Pre-2018 CSE ID: CS2002-0724

The traditional university campus is designed to foster a thriving com-munity of learners, but modernity has introduced many stresses. Mobile comput-ing holds the potential to strengthen a campuss traditional institutions of com-munity through a process of indirect mediation. This paper introduces Active-Campus, a suite of personal services for sustaining an educational community. The design and implementation of ActiveCampus is described, which is now in deployment on the UCSD campus.Pre-2018 CSE ID: CS2002-0714