John W. Cooper

Calibration results for NOAA-11 AVHRR channels 1 and 2 from congruent path aircraft observations

Abstract A method for using congruent atmospheric path aircraft-satellite observations to calibrate a satellite radiometer is presented. A calibrated spectroradiometer aboard a NASA ER-2 aircraft at an altitude of 19 km above White Sands, New Mexico, was oriented to view White Sands at the overpass time of the NOAA-11 Advanced Very High Resolution Radiometer (AVHRR) instrument along the same view vector as the satellite instrument. The data from six flights between November 1988 and October 1990 were transformed into corresponding estimates of AVHRR channel radiance at the satellite (derived from the aircraft measurements), and average counts (from the AVHRR measurements), both averaged across the footprint of the spectroradiometer. Prelaunch measurements of the AVHRR spectral response profiles are assumed, and the radiance spectrum measured by the spectroradiometer was adjusted to satellite altitude using the LOWTRAN-7 computer code. Spatial misregistration of the two flight datasets was corrected by max...

Characterization of errors in the use of integrating-sphere systems in the calibration of scanning radiometers

Laboratory measurements were performed to characterize the geometrical effects in the calibration of the NASAs cloud absorption radiometer (CAR). The measurements involved three integrating sphere sources (ISSs) operated at different light levels and experimental setups to determine radiance variability. The radiance gradients across the three ISS apertures were 0.2%-2.6% for different visible, near-infrared, and shortwave infrared illumination levels but <15% in the UV. Change in radiance with distance was determined to be 2%-20%, being highest in the UV. Radiance variability due to the edge effects was found to be significant; as much as 70% due to the sphere aperture and <10% due to the CAR telescopes secondary mirror.

Comparison of spectral radiance calibrations at oceanographic and atmospheric research laboratories

This report describes the first Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Radiometric Intercomparison (SIMRIC-1). The purpose of the SIMRIC-1 is to ensure a common radiometric scale among the calibration facilities that are engaged in calibrating in situ radiometers used for ocean colour-related research and to document the calibration procedures and protocols. SIMBIOS staff visited the seven participating laboratories for at least two days each. The SeaWiFS Transfer Radiometer (SXR-II) measured the calibration radiances produced in the laboratories. The measured radiances were compared with the radiances expected by the laboratories. Typically, the measured radiances were higher than the expected radiances by 0 to 2%. This level of agreement is satisfactory. Several issues were identified where the calibration protocols need to be improved, especially the reflectance calibration of the reference plaques and the distance correction when using the irradiance standards at distances greater than 50?cm. The responsivity of the SXR-II changed from 0.3% (channel 6) to 1.6% (channel 2) from December 2000 to December 2001. Monitoring the SXR-II with a portable light source showed a linear drift of the calibration, except for channel 1, where a 2% drop occurred in summer.

Radiometric measurement comparisons using transfer radiometers in support of the calibration of NASA's Earth Observing System (EOS) sensors

EOS satellite instruments operating in the visible through the shortwave infrared wavelength regions (from 0.4 micrometer to 2.5 micrometer) 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 Administrations (NASAs) 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 National Institute of Standards and Technology, the University of Arizona Optical Sciences Center Remote Sensing Group, NASAs Goddard Space Flight Center, and the National Research Laboratory of Metrology 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 plus or minus 3% to plus or minus 5% range. Preliminary results reported during eleven radiometric measurement comparisons held between February 1995 and May 1998 have shown the radiance of integrating spheres agreed to within plus or minus 2.5% from the average at blue wavelengths and to within plus or minus 1.7% 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.

Calibration of a radiance standard for the NPP/OMPS instrument

In June 2007, a spherical integrating source was calibrated in the National Aeronautics and Space Administration (NASA) Goddard Space Flight Centers (GSFC) Calibration Facility as part of the prelaunch characterization program for the NPOESS Preparatory Program (NPP) Ozone Mapping and Profiler Suite (OMPS) instrument. Before shipment to the instrument vendor, the sphere radiance was measured at the Remote Sensing Laboratory at the National Institute of Standards (NIST) and then returned to the NASA Goddard facility for a second calibration. For the NASA GSFC calibration, the reference was a set of quartz halogen lamps procured from NIST. For the measurement in the Remote Sensing Laboratory, the reference was an integrating sphere that was directly calibrated at NISTs Facility for Spectroradiometric Calibrations (FASCAL). For radiances in the visible and near-infrared (400 nm to 1000 nm), the agreement between the NASA GSFC calibration and the validation measurements at the Remote Sensing Laboratory was at the 1 % level. For radiances in the near ultraviolet (250 nm to 400 nm), the agreement was at the 3 % level.

Radiometric Gains Of Satellite Sensors Of Reflected Soliar Radiation: Results From Nasa Er-2 Aircraft Measurements

A method for using congruent aircraft-satellite observations to calibrate a satellite sensor is presented. A calibrated spectroradiometer at an altitude of 19 km above White Sands, NM, is oriented to view White Sands at the satellite overpass time along the same view vector as the satellite sensor. Collected data are transformed into corresponding estimates of sensor band radiance at the satellite (derived from the aircraft measurements), and average count (from the sensor measurements). These are both averaged across the footprint of the spectroradiometer. Results are presented for the evolution of NOAA-11 Advanced Very High Resolution Radiometer (AVHRR) (Bands 1 and 2) gain between November 1988 and October 1990, and for GOES-6 and GOES-7 VISSR/VAS visible bands during the same period. Estimates of uncertainty in the results are presented, as well as ideas for their reduction in future flights.

Characterization and application of a LED-driven integrating sphere source

A Light-Emitting Diode (LED)-driven integrating sphere light source has been fabricated and assembled in the NASA Goddard Space Flight Center (GSFC) Code 618 Biospheric Sciences Laboratory’s Calibration Facility. This light source is a 30.5 cm diameter integrating sphere lined with Spectralon. A set of four LEDs of different wavelengths are mounted on the integrating sphere’s wall ports. A National Institute of Standards and Technology (NIST) characterized Si detector is mounted on a port to provide real-time monitoring data for reference. The measurement results presented here include the short-term and long-term stability and polarization characterization of the output from this LED-driven integrating sphere light source. As an initial application, this light source is used to characterize detector/pre-amplifier gain linearity in light detection systems. The measurement results will be presented and discussed.

Characterization of a radiometric monitoring system for NASA code 618's SIRCUS-G

A tunable, intensity-stabilized, quasi-continuous wave (CW) laser system, patterned after the Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) system at the National Institute of Standards and Technology (NIST) 1, has been installed and is being tested in the NASA Goddard Space Flight Center (GSFC) Code 618 Biospheric Sciences Laboratory’s Calibration Facility. This system is referred to as SIRCUS-G (SIRCUS-Goddard). The tunable output of the laser system is fiber-fed to a 76.2 cm diameter integrating sphere lined with Spectralon. The uniform radiance light emitted from the integrating sphere is used in system-level radiometric responsivity characterizations and wavelength calibrations of remote sensing instruments. The primary radiance reference standards in the responsivity characterizations are a three-element Si trap radiometer for the visible and near infrared and a radiometer employing an InGaAs detector. Both radiometers have been calibrated by NIST. These radiometers are located at the exit port of the Spectralon coated integrating sphere. In addition, a set of three radiometers are mounted on the 76.2 cm integrating sphere’s wall ports to monitor source radiance and to provide real-time sphere radiance data during the calibrations of remote sensing instruments. These monitor radiometers provide spectral coverage from 300nm to near 2500nm. This paper presents the results of our characterization of the performance of these monitor radiometers. Results are presented and discussed on monitor radiometer short- and long-term system stability, noise level, and total measurement uncertainty.

Integrating sphere source monitoring and stability data

Two critical requirements of any calibration source are short and long-term operational stability and repeatability. Source monitoring is necessary in quantifying overall source performance including stability and repeatability. The NASA GSFC Code 920.1 Radiance Calibration Facility (RCF) developed a Filter Radiometer Monitoring System (FRMS) to continuously monitor the performance of its integrating sphere calibration sources. FRMS bands are in the 0.4 -2.4 μm region, with several bands selected to coincide with common remote sensing bands. The FRMS was designed and fabricated in the year 2000. Early in 2001, the FRMS was reconfigured prior to being deployed on the RCF 180cm integrating sphere. This paper describes the instrument modifications resulting from the FRMS reconfiguration and presents FRMS monitor data for three RCF integrating sphere sources.

Characterizations of a KHz pulsed laser detection system.

A KHz Pulsed Laser Detection System was developed employing the concept of charge integration with an electrometer, in the NASA Goddard Space Flight Center, Code 618 Calibration Lab for the purpose of using the pulsed lasers for radiometric calibration. Comparing with traditional trans-impedance (current-voltage conversion) detection systems, the prototype of this system consists of a UV-Enhanced Si detector head, a computer controlled shutter system and a synchronized electrometer. The preliminary characterization work employs light sources running in either CW or pulsed mode. We believe this system is able to overcome the saturation issue when a traditional trans-impedance detection system is used with the pulsed laser light source, especially with high peak-power pulsed lasers operating at kilohertz repetition rates (e.g. Ekspla laser or KHz OPO). The charge integration mechanism is also expected to improve the stability of measurements for a pulsed laser light source overcoming the issue of peak-to-peak stability. We will present the system characterizations including signal-to-noise ratio and uncertainty analysis and compare results against traditional trans-impedance detection systems.