Radiometric Calibration Facility Research Articles

Measurement of the Point Response Functions of CERES Scanning Radiometers

Some applications of data from the Clouds and the Earth's Radiant Energy System (CERES) scanning radiometer require the use of the point response function (PRF), which describes the influence of radiance from each point on the measurement. A radiance source for the measurement of the PRF of the CERES instruments was built and installed into the Radiometric Calibration Facility, in which the CERES instruments have been calibrated. The design and application of the PRF source and the computation of the PRF from these measurements are described. In order to compare the PRF based on measurements with the theoretical PRF, it is necessary to account for the finite size of the beam from the source. The use of the PRF source and the analysis of the data are demonstrated by application to the FM-5 instrument. The measured results compare well with theory for the CERES instruments and are presented for FM-5.

Performance and Long-Term Stability of the Prelaunch Radiometric Calibration Facility for the Clouds and the Earth's Radiant Energy System Instruments

The Radiometric Calibration Facility (RCF) at Northrop Grumman Aerospace Systems was used between 1995 and 2008 to establish the prelaunch calibration of the first six Clouds and the Earth's Radiant Energy System (CERES) instruments, with the seventh CERES instrument scheduled to be tested in the RCF in 2012. This paper reviews the performance of the RCF radiometric standards, which are the narrow-field blackbody (NFBB) and the short-wave reference source, as well as the RCF transfer active-cavity radiometer, in the context of the CERES prelaunch calibration process. A detailed investigation of the long-term stability of these standards over the 1999-2008 time span of CERES FM5 testing is reported, showing that the RCF calibrations in the long and short waves have remained stable relative to the NFBB absolute reference at levels of 0.06% and 0.5%, respectively, over the eight-year span.

A new methodology for in-flight radiometric calibration of the MIVIS imaging sensor

Sensor radiometric calibration is of great importance in computing physical values of radiance of the investigated targets, but often airborne scanners are not equipped with any in-flight radiometric calibration facility. Consequently, the radiometric calibration or airborne systems usually relies only on pre-flight and vicarious calibration or on indirect approaches. This paper introduces an experimental approach that makes use of on-board calibration techniques to perform the radiometric calibration of the CNR’s MIVIS (Multispectral Infrared and Visible Imaging Spectrometer) airborne scanner. This approach relies on the use of an experimental optical test bench originally designed at Politecnico di Milano University (Italy), called MIVIS Flying Test Bench (MFTB), to perform the first On-The-Fly (OTF) calibration of the MIVIS reflective spectral bands. The main task of this study is to estimate how large are the effects introduced by aircraft motion (e.g., e.m. noise or vibrations) and by environment conditions (e.g., environment temperature) on the radiance values measured by the MIVIS sensor during the fly. This paper describes the first attempt to perform an On-The-Fly (OTF) calibration of the MIVIS reflective spectral bands (ranging from 430 nm to 2.500 nm). Analysis of results seems to point out limitations of traditional radiometric calibration methodology based only on pre-flight approaches, with important implications for data quality assessment.

Deployment test of the NIST EOS Thermal-infrared Transfer Radiometer

The National Institute of Standards and Technology (NIST) Thermal-infrared Transfer Radiometer (TXR), developed for the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS), was deployed at the remote sensing radiometric calibration facility at Los Alamos National Laboratory (LANL). The purpose of the deployment was to test the ability of the TXR to operate off-site of NIST in a host cryogenic vacuum chamber, and to provide an end-to-end verification of the radiance scale in the LANL facility. The TXR was calibrated pre-trip and post-trip at NIST against a water bath black body in ambient conditions. At LANL, the TXR was operated in a liquid nitrogen cooled vacuum chamber, mounted in the same position that remote sensing instruments occupy during their pre-flight calibrations. The results from the TXR 5 µm channel show that the LANL radiance scale agrees with that of the NIST water bath black body to within a radiance uncertainty of - 0.16% ( k = 2). This corresponds to a brightness temperature uncertainty of 50 mK ( k = 2) at 300 K. Thus, the TXR has demonstrated its ability to provide an economical end-to-end system-level verification of the component-level radiometric scale assigned to a calibration facility. Such verifications provide an extra level of confidence in the radiometric accuracy of flight instrument calibration facilities that has hitherto not been possible.

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

The CERES instrument has three radiometers which operate in the short-wave (0,3 μm to 5 μm), the long-wave (8 μm to 12 μm) and total broadband (0,3 μm to >200 μm) spectral regions. The long-wave calibration plan for CERES provides for absolute radiometric calibration of the two CERES sensors operating in the long-wave portion of the spectrum. Ground calibration is carried out in the TRW Radiometric Calibration Facility (RCF), a cryogenic vacuum chamber with the capability to simulate radiometrically both cold space and Earth viewing conditions. Absolute calibration is made using a temperature-based radiometric scale created by a black-body radiance standard controlled at temperatures from 200 K to 320 K. In May 1992, the CERES radiometric test model (RTM), a developmental but functionally flight-like instrument, was calibrated at TRW in the RCF. This was the first end-to-end long-wave calibration of a CERES sensor and provided a test and initial validation of the long-wave calibration plan and procedures. The gain, offset, out-of-field response and spectral response were determined for each sensor. The end-to-end long-wave calibration plan is described and the RTM calibration and validation results are presented.

Synchrotron ultraviolet radiation facility (SURF II) radiometric instrumentation calibration facility

Spectrometer calibrations have been performed at the National Institute of Standards and Technology (formerly the National Bureau of Standards) for over 10 yr using the calculable synchrotron radiation from the SURF II electron storage ring. SURF II is now a high-performance storage ring that can operate at electron energies up to 300 MeV and with over 250 mA of stored current. One beam line, operationally supported by the National Aeronautics and Space Administration (NASA), is dedicated for use as a radiometric instrumentation calibration facility for outside users.