<title>Enhancements to the radiometric calibration facility for the Clouds and the Earth's Radiant Energy System instruments</title>

Abstract

The Earth Radiation Budget Experiment (ERBE) instruments, developed by NASA's Langley Researctt Center and TRW, were first launched on the Earth Radiation Balance Satellite (ERBS) on October 5, 1984 and launched subsequentlyon NOAA-9 and NOAA-10. The radiometric calibration of ERBE instruments was performed at TRW in a cryogenic vacuum chamber developed specifically for that purpose. During calibration each instrument was mounted on a carousel located at the center of the chamber. Broadband calibration sources covering the wavelength range from 0.3 um to >50 um were located around the chamber perimeter. The required absolute radiometric error bounds for the ERBE scanner instruments were +1-3.5% in the shortwave (0.3 urn to 3.5 urn), +1-2.0% in the longwave (5 urn to >50 urn), and +1-1.7% in the total (0.3 urn to >50 urn) bands.1The performance of this facility is being enhanced significantly in preparation for calibration of the Clouds and the Earth's RadiantEnergy System (CERES) instruments. Absolute radiometericcalibrationerror boundsfor the CERES instrument are +1-1% in the shortwave band and +1-. 0.5% longwave and total bands. Enhancements include a new blackbody source, a complete re-design of the shortwave reference source, and a new cryogenic active cavity radiometer (ACR) developed by Cambridge Research and Instrumentation, Inc. The ACR will be used to transfer calibration from the longwave blackbody source to the shortwave reference source. In addition, the master reference blackbody used as the radiometric standard for calibrating ERBE and space simulation equipment including LN2 cooled space references and two albedo plates for Earth simulation are being upgraded. and monitor the environmental conditions within the vacuum chamber. The overall layout of the Radiometric Calibration Facility is shown in figure 2. 0-8194-0602-3/91/$4.O0

Pre-launch characterization of spectral response functions for the Clouds and Earth's Radiant Energy System (CERES) instrument sensors

“…2, was used to calibrate the CERES sensors as well as to determine the shortwave spectral response 8 . The response in the shortwave was determined using the Shortwave Reference Source (SWRS), the Transfer Active Cavity Radiometer (TACR) for traceability of the shortwave radiances and the Narrow Field Blackbody (NFBB) for absolute calibration.…”

<title>Far-IR spectral response measurements of the Clouds and the Earth's Radiant Energy System (CERES) sensors using a Fourier transform spectrometer and pyroelectric reference detector</title>

“…LV 1/(2 * the physical travel length in cm). (6) The dynamic range ofthe mterferogram which impacts signal to noise ofthe measurement is given by the product of the dynamic range in the spectrum to be measured and the square root of the number of resolution elements in the spectrum being scanned 8• Therefore, greater resolution requires both greater signal to noise and longer scan times. For the CERES scans, the highest required resolution is 1 cm1 and this requirement applies from 200 to 50cm1 where signals are lowest.…”

“…In response to these tighter requirements, enhancements have been made to the RCF and the CERES calibration plan and these have been described , 6 Because 3.8 % of the energy of a 275 K blackbody is at wavelengths longer than 50 tm, it is necessary for accurate calibration to have fairly precise spectral response characterization of the total channel radiometer which remains quite responsive out beyond 200 pm '. Also, the other two channels have longwave leaks to the nominal passbands.…”

Clouds and the Earth's Radiant Energy System (CERES): Long-wave Calibration Plan and Radiometric Test Model (RTM) Calibration Results

“…The absolute reference standard used for LW calibration of the ERBE scanning and non-scanning sensors is referred to as the wide field black body (WFBB) because it was designed to provide calibration for the nearly hemispherical view of the ERBE non-scanning cavity detectors. Its design incorporates 2,5 cm deep circular grooves for high emittance over a 12,5 cm diameter aperture [6]. CERES retains this black body and adds the NFBB with performance optimized for the relatively narrow field-of-view (FOV) of the CERES scanning sensors.…”