David I. Gellman

Vicarious Radiometric Calibrations of EOS Sensors

Abstract Four methods for the in-flight radiometric calibration and cross calibration of multispectral imaging sensors are described. Three make use of ground-based reflectance, irradiance, and radiance measurements in conjunction with atmospheric measurements and one compares calibrations between sensors. Error budgets for these methods are presented and their validation is discussed by reference to SPOT and TM results and shown to meet the EOS requirements in the solar-reflective range.

Uncertainties in the in-flight calibration of sensors with reference to measured ground sites in the 0.4-1.1 μm range

Abstract This article describes the error sources for three in-flight sensor calibration methods used by the Remote Sensing Group of the Optical Sciences Center at the University of Arizona. The three methods are the reflectance-, improved reflectance-, and radiance-based methods, which all reference the earth-atmosphere system. The sources of error or uncertainty for each method are discussed, and an estimate of the percent uncertainty associated with each source is made for conditions similar to those actually used for calibrations at White Sands, New Mexico. The results of in-flight calibrations are compared to those of the on-board lamp calibration system for a SPOT HRV camera.

Improved evaluation of optical depth components from langley plot data

Abstract A simple, iterative procedure to determine the optical depth components of the extinction optical depth measured by a solar radiometer is presented. Simulated data show that the iterative procedure improves the determination of the exponent of a Junge law particle size distribution. The determination of the optical depth due to aerosol scattering is improved as compared to a method which uses only two points from the extinction data. The iterative method was used to determine spectral optical depth components for 11–13 June 1988 during the MAC III experiment.

Obtaining Surface Reflectance Factors from Atmospheric and View Angle Corrected SPOT-1 HRV Data

Abstract SPOT-1 High-Resolution Visible (HRV) multispectral (XS) and panchromatic data were acquired over an agricultural area on two consecutive days in June 1987, June 1988, and April 1989, at view zenith angles of approximately 23° and 10°. Digital data were converted to surface reflectance factors ( ρ s ) by use of the sensor calibration coefficients, measurements of atmospheric optical depth, and a radiative transfer model. View-angle corrections (Cv) were derived from ground-based measurements of bidirectional radiance of bare soil, and used to convert nadir ground- and aircraft-based measurements to off-nadir values ( ρ g and ρ a , respectively) for comparison with SPOT HRV data. The absolute error of ρ s values, relative to ρ g and ρ a , was less than 10% for most XS bands on all six days over the reflectance range 0.1-0.4. However, there was a systematic trend for ρ s estimates to be slightly higher than ρ g and ρ a measurements, particularly at low surface reflectances. The Cv coefficients were then applied to SPOT HRV data for a variety of cover types to assess the effectiveness of a simple, view-angle correction over a complex landscape. For rough, unvegetated surfaces, ρ s values that had originally differed by more than 0.09 in reflectance on the two days were brought to within 0.01 in all three XS bands. For vegetated surfaces, Cv appeared to be wavelength dependent; the soil-based Cv worked well for data in the red and green wavebands but overcorrected the near-IR data. The Cv correction overcompensated for view angle effects over planar surfaces (i.e., water and roads) in all wavebands.

In-flight radiometric calibration of Landsat-5 Thematic Mapper from 1984 to the present

The reflectance-based method is used to determine an absolute radiometric calibration of Landsat-5 Thematic Mapper for the solar reflective portion of the spectrum. Results are given for data collected at White Sands Missile Range in New Mexico on 1992-08-15. These results are compared to those obtained from applying a similar processing approach to data collected in 1984, 1985, 1987, and 1988.

Calibrated intercepts for solar radiometers used in remote sensor calibration

Calibrated solar radiometer intercepts allow spectral optical depths to be determined for days with intermittently clear skies. This is of particular importance on satellite sensor calibration days that are cloudy except at the time of image acquisition. This paper describes the calibration of four solar radiometers using the Langley-Bouguer technique for data collected on days with a clear, stable atmosphere. Intercepts are determined with an uncertainty of less than six percent, corresponding to a maximum uncertainty of 0.06 in optical depth. The spread of voltage intercepts calculated in this process is carried through three methods of radiometric calibration of satellite sensors to yield an uncertainty in radiance at the top of the atmosphere of less than one percent associated with the uncertainty in solar radiometer intercepts for a range of ground reflectances.

Review of SPOT-1 and -2 calibrations at White Sands from launch to the present

Since their launch in February 1986 and January 1990, we have, from time to time, conducted radiometric calibrations of the SPOT-1 and -2 Haute Resolution Visible (HRV) cameras at White Sands, New Mexico. We summarize the results of the calibrations, comparing the absolute calibration coefficients obtained from the White Sands data to the relative calibrations obtained from the on-board tungsten lamp.

Radiometric calibration of SPOT 2 HRV - A comparison of three methods

Three methods for determining an absolute radiometric calibration of a spacecraft optical sensor are compared. They are the well-known reflectance-based and radiance-based methods and a new method based on measurements of the ratio of diffuse-to-global irradiance at the ground. The latter will be described in detail and the comparison of the three approaches will be made with reference to the SPOT-2 HRV cameras for a field campaign 1990-06-19 through 1990-06-24 at the White Sands Missile Range in New Mexico.

In-flight radiometric calibration of ASTER by reference to well-characterized scenes

ASTER will be calibrated in the laboratory by reference to sources traceable to NRLM and NIST standards and through the use of transfer radiometers. Partial aperture on-board calibration systems will be used in the solar-reflective range and an on-board blackbody source will be used in the infrared. An important independent source of calibration data will be provided through the in-flight radiometric calibration of ASTER by reference to well- characterized scenes. The latter is the subject of this paper. Methods that make use of ground reflectance and radiance measurements made simultaneously with atmospheric measurements at selected sites and used as input to radiative transfer codes are described. The results of error analyses are presented indicating that, depending on the method used, the predicted uncertainties fall between +/- 2.8% and +/- 4.9%, for the solar-reflective range. In the thermal infrared, the goal is an uncertainty of less than 1 K. A method that provides in-flight cross calibrations with other sensors also is described.

Radiometric calibration of an airborne multispectral scanner

The absolute radiometric calibration of the NS001 Thematic Mapper Simulator reflective channels was examined based on laboratory tests and in-flight comparisons to ground measurements. The NS001 data are calibrated in-flight by reference to the NS001 internal integrating sphere source. This sources power supply or monitoring circuitry exhibited greater instability in-flight during 1988-1989 than in the laboratory. Extrapolating laboratory behavior to in-flight data resulted in 7-20 percent radiance errors relative to ground measurements and atmospheric modeling. Assuming constancy in the sources output between laboraotry and in-flight resulted in generally smaller errors. Upgrades to the sources power supply and monitoring circuitry in 1990 improved its in-flight stability, though in-flight ground reflectance based calibration tests have not yet been performed.