Intercalibration of Microwave Radiometer Brightness Temperatures for the Global Precipitation Measurement Mission (original) (raw)
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2014 13th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 2014
The NASA's Global Precipitation Measurement (GPM) mission uses a constellation of international satellites with microwave radiometers, to provide the next-generation of global observations of precipitation. The GPM Intersatellite Calibration Working Group (aka XCAL) has the responsibility to perform the radiometric calibration process to normalize all radiometers to a common source, the GPM Microwave Imager, which serves as a radiometric transfer standard. Prior to the launch of GPM instrument on February 28, 2014, the Tropical Rainfall Measurement Mission (TRMM) Microwave Imager has been used as a proxy for the GMI to develop procedures and data analysis algorithms for inter-comparing two similar, but not identical, radiometers. In this regard, this paper assesses the long-term radiometric calibration stability of TMI relative to WindSat polarimetric radiometer. CFRSL conducted two independent inter-comparisons over oceans in XCAL year (July 2005-June 2006) and C Y 2011, and results are presented, which demonstrate deciKelvin relative stability over this greater than five-year period.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2012
The double difference method of inter-calibration between spaceborne microwave radiometers is combined with the vicarious cold calibration method for calibrating an individual radiometer. Vicarious cold calibration minimizes the effects of geophysical variability on radiative transfer models (RTMs) of the brightness temperature (TB) data and it accounts for frequency and incidence angle dissimilarity between radiometers. Double differencing reduces the sensitivity of the inter-calibration to RTM error and improper accounting for geophysical variables in the RTM. When combined together, the two methods significantly improve the confidence with which calibration differences can be identified and characterized. This paper analyzes the performance of the vicarious cold calibration double difference method for conical scanning microwave radiometers and quantifies the improvement this method provides compared to performing a simpler inter-calibration by direct comparison of radiometer measurements.
A new approach for radiometric cross calibration of satellite-borne radiometers
Proceedings. 2005 IEEE International Geoscience and Remote Sensing Symposium, 2005. IGARSS '05., 2005
Approaches for establishing the absolute calibration of a newly deployed, satellite-borne radiometer have varied from aircraft under flights with previously calibrated sensors to vicarious calibration over known, benign backgrounds, utilizing radiative transfer models to generate top-of-atmosphere radiances. In this paper, we demonstrate the efficacy of this approach by presenting results of the crosscomparison of two sensors that are known to be well calibrated, Atmospheric Infrared Sounder (AIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS). We focus on the results of the cross-comparison between MODIS and AIRS for the ranges of atmospheric and surface conditions embodied in a variety of common Earth scenes in this paper. We also investigate the dependence of the quality of the cross-calibration process as a function of the surface emissivity spectrum, phenomenology, and atmospheric conditions, identifying under what conditions the cross-calibration process is effective.
Intercalibration of the GPM Microwave Radiometer Constellation
Journal of Atmospheric and Oceanic Technology, 2016
The Global Precipitation Measurement (GPM) mission is a constellation-based satellite mission designed to unify and advance precipitation measurements using both research and operational microwave sensors. This requires consistency in the input brightness temperatures (Tb), which is accomplished by intercalibrating the constellation radiometers using the GPM Microwave Imager (GMI) as the calibration reference. The first step in intercalibrating the sensors involves prescreening the sensor Tb to identify and correct for calibration biases across the scan or along the orbit path. Next, multiple techniques developed by teams within the GPM Intersatellite Calibration Working Group (XCAL) are used to adjust the calibrations of the constellation radiometers to be consistent with GMI. Comparing results from multiple approaches helps identify flaws or limitations of a given technique, increase confidence in the results, and provide a measure of the residual uncertainty. The original calibration differences relative to GMI are generally within 2-3 K for channels below 92 GHz, although AMSR2 exhibits larger differences that vary with scene temperature. SSMIS calibration differences also vary with scene temperature but to a lesser degree. For SSMIS channels above 150 GHz, the differences are generally within ;2 K with the exception of SSMIS on board DMSP F19, which ranges from 7 to 11 K colder than GMI depending on frequency. The calibrations of the cross-track radiometers agree very well with GMI with values mostly within 0.5 K for the Sondeur Atmosphérique du Profil d'Humidité Intertropicale par Radiométrie (SAPHIR) and the Microwave Humidity Sounder (MHS) sensors, and within 1 K for the Advanced Technology Microwave Sounder (ATMS).
2013 IEEE International Geoscience and Remote Sensing Symposium - IGARSS, 2013
The effect of inter-calibration on a Level 3 rainfall product for the Global Precipitation Measurement (GPM) mission is examined using two spaceborne microwave radiometers that are currently used to derive rain measurements, the Tropical Rainfall Measuring Mission Microwave Imager (TMI) and the Special Sensor Microwave/Imager (SSM/I). It is found that inter-calibrating the microwave radiometer brightness temperatures from the two instruments improves the agreement of the derived rain accumulations between the two radiometers. The average difference between TMI and F13 derived rain accumulations is 0.60 mm/day before intercalibration is applied. This difference decreases to 0.08 mm/day when F13 is inter-calibrated to TMI.
Sensors, Systems, and Next-Generation Satellites Iii, 1999
EOS satellite instruments operating in the visible through the shortwave infrared wavelength regions (from 0.4 tm to 2.5 tm) are calibrated prior to flight for radiance response using integrating spheres at a number of instrument builder facilities. The traceability of the radiance produced by these spheres with respect to international standards is the responsibility of the instrument builder, and different calibration techniques are employed by those builders. The National Aeronautics and Space Administration's (NASA's) Earth Observing System (EOS) Project Science Office, realizing the importance of preflight calibration and cross-calibration, has sponsored a number of radiometric measurement comparisons, the main purpose of which is to validate the radiometric scale assigned to the integrating spheres by the instrument builders. This paper describes the radiometric measurement comparisons, the use of stable transfer radiometers to perform the measurements, and the measurement approaches and protocols used to validate integrating sphere radiances. Stable transfer radiometers from the in Japan, have participated in these comparisons. The approaches used in the comparisons include the measurement of multiple integrating sphere lamp levels, repeat measurements of select lamp levels, the use of the stable radiometers as external sphere monitors, and the rapid reporting of measurement results. Results from several comparisons are presented. The absolute radiometric calibration standard uncertainties required by the EOS satellite instruments are typically in the to range. Preliminary results reported during eleven radiometric measurement comparisons held between February 1 995 and May 1 998 have shown the radiance of integrating spheres agreed to within from the average at blue wavelengths and to within .7% from the average at red and near infrared wavelengths. This level of agreement lends confidence in the use of the transfer radiometers in validating the radiance scales assigned by EOS instrument calibration facilities to their integrating sphere sources.
Long-term stability of ERS-2 and TOPEX microwave radiometer in-flight calibration
IEEE Transactions on Geoscience and Remote Sensing, 2005
The microwave radiometers on altimeter missions are specified to provide the "wet" troposphere path delay with an uncertainty of 1 cm or lower, at the location of the altimeter footprint. The constraints on the calibration and stability of these instruments are therefore particularly stringent. The paper addresses the questions of long-term stability and absolute calibration of the National Aeronautics and Space Administration Topography Experiment (TOPEX) and European Space Agency European Remote Sensing 2 (ERS-2) radiometers over the entire range of brightness temperatures. Selecting the coldest measurements over ocean from the two radiometers, the drift of the TOPEX radiometer 18-GHz channel is confirmed to be about 0.2 K/year over the seven first years of the mission, and the one of the ERS-2 radiometer 23.8-GHz channel to be 0 2 K/year.
Field Intercomparison of Radiometers Used for Satellite Validation in the 400–900 nm Range
Remote Sensing
An intercomparison of radiance and irradiance ocean color radiometers (the second laboratory comparison exercise—LCE-2) was organized within the frame of the European Space Agency funded project Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) May 8–13, 2017 at Tartu Observatory, Estonia. LCE-2 consisted of three sub-tasks: (1) SI-traceable radiometric calibration of all the participating radiance and irradiance radiometers at the Tartu Observatory just before the comparisons; (2) indoor, laboratory intercomparison using stable radiance and irradiance sources in a controlled environment; (3) outdoor, field intercomparison of natural radiation sources over a natural water surface. The aim of the experiment was to provide a link in the chain of traceability from field measurements of water reflectance to the uniform SI-traceable calibration, and after calibration to verify whether different instruments measuring the same object provide results consistent within the ...
A Time-Varying Radiometric Bias Correction for the TRMM Microwave Imager
IEEE Transactions on Geoscience and Remote Sensing, 2000
Recent intersatellite radiometric comparisons of the Tropical Rainfall Measurement Mission Microwave Imager (TMI) with polar orbiting satellite radiometer data and modeled clearsky radiances have uncovered a time-variable radiometric bias in the TMI brightness temperatures. The bias is consistent with a source that generally cools during orbit night and warms during sunlight exposure. The likely primary source has been identified as a slightly emissive parabolic antenna reflector. This paper presents an empirical brightness temperature correction to TMI based on the position around each orbit and the Sun elevation above the orbit plane. The results of radiometric intercomparisons with WindSat and special sensor microwave imager are presented, which demonstrate the effectiveness of the recommended correction approach based on four years of data.