Calibrating the GOES Imager visible channel using the moon as an irradiance source

Abstract

An activity is underway to establish the feasibility of using the Moon as an irradiance standard to calibrate the visible channel (0.55-0.75 micrometers) ofthe GOES Imagers. This channel is calibrated prior to launch but there are no facilities in the instrument for in-flight calibration ofthe visible band. The Moon is within the Imager field of view for a few days every month and can thus be observed by the GOES Imager with reasonable illumination conditions with a minimum disturbance of the operational observations. This makes it relatively easy to compare instruments on different GOES satellites because ofthe small change in illumination angles and look angles between properly timed observations. In a separate NASA-sponsored program, ground-based telescopic measurements ofthe Moon are being made in several spectral bands between 0.34 and 0.95 micrometers to establish the Moon as a spectral radiance standard over a wide range of illumination and libration angles. Histograms of images of the moon can be converted to total lunar irradiance using prelaunch calibration. This will eventually be compared with the predicted total radiance from the moon from ground measurement to update the calibration. There are over 1 00,000 pixels in a GOES image of a full Moon, which enables a precise measurement. Imager test data from GOES 10 was analyzed and preliminary estimates ofthe performance of the two different analysis approaches are presented. This paper includes a comparison ofthe relative calibration ofthe Moon at two times, a few days apart, which have significant changes in the Moon's illumination. This data is used to assess the ability of the model to track these changes assuming the instrument was stable over these few days. Further work will be required to improve performance of the analysis of the space data, in the ground model and in the use of this type of data to make an absolute calibration of the Imager.

<title>Use of the moon for spacecraft calibration over 350 to 2500 nm</title>

“…25 Although the large number of image pixels on the Moon allows precise recovery of the instrument response to Lunar irradiance, the reduced data exhibit about 5% scatter relative to the current ROLO irradiance model; the cause of this is unknown.…”

On-Orbit Radiance Calibration of Nighttime Sensor of LuoJia1-01 Satellite Based on Lunar Observations

“…A lunar calibration method for remote sensing satellite sensors using lunar spectral irradiance measurement of the ROLO model has been established by the USGS (U.S. Geological Survey), and has been successfully applied to the GMS-5 (Geostationary Meteorological Satellite) [27,28], GOES (Geostationary Operational Environmental Satellite) [29][30][31], Suomi-NPP [18,[32][33][34][35][36][37][38][39], SeaWIFS (The Sea-Viewing Wide Field-of-View Sensor) [40][41][42][43], and other instruments for on-orbit radiometric calibration and stability monitoring. Fujisada et al [28] calibrated the radiance of the GMS-5 remote sensing sensor based on pairs of GMS-5 lunar observation and ROLO images captured under the same observation conditions.…”

Measurements of filtered lunar radiances using the NASA Terra spacecraft/CERES thermistor bolometer sensors during 2000 and 2001

“…[2][3][4][5][6][7][8][9][10][11][12][13] The lunar reflecting surface is estimated to be photometrically stable at the 10 -5 % per year level. 2 The incoming total solar irradiance (TSI)/radiance, projected on the moon, was measured at the 0.1% stability level 14,15 between 1984 and 2003. Therefore, moon-reflected radiances should be stable at precision levels approaching 0.1%, if the radiance variations with phase angle, libration, and wavelength corrections are included.…”