Comparison of SeaWiFS measurements of the Moon with the US Geological Survey lunar model

Abstract

The Sea-Viewing Wide-Field-of-View Sensor (SeaWiFS) has made monthly observations of the Moon since 1997. Using 66 monthly measurements, the SeaWiFS calibration team has developed a correction for the instrument's on-orbit response changes. Concurrently, a lunar irradiance model has been developed by the U.S. Geological Survey (USGS) from extensive Earth-based observations of the Moon. The lunar irradiances measured by SeaWiFS are compared with the USGS model. The comparison shows essentially identical response histories for SeaWiFS, with differences from the model of less than 0.05% per thousand days in the long-term trends. From the SeaWiFS experience we have learned that it is important to view the entire lunar image at a constant phase angle from measurement to measurement and to understand, as best as possible, the size of each lunar image. However, a constant phase angle is not required for using the USGS model. With a long-term satellite lunar data set it is possible to determine instrument changes at a quality level approximating that from the USGS lunar model. However, early in a mission, when the dependence on factors such as phase and libration cannot be adequately determined from satellite measurements alone, the USGS model is critical to an understanding of trends in instruments that use the Moon for calibration. This is the case for SeaWiFS.

Satellite Instrument Calibration for Measuring Global Climate Change: Report of a Workshop

“…One method that has been successfully implemented for the reflected solar spectral interval is lunar observations, from orbit, with the sensor. One example is the ocean color satellite Sea-viewing Wide Field-of-View Sensor (SeaWiFS), which used lunar observations to correct for degradation in the near-infrared channels (Barnes et al 2004). The required reference lunar reflectance data are being supplied by a dedicated ground-based facility (Anderson et al 1999).…”

Coloration determination of spectral darkening occurring on a broadband Earth observing radiometer: application to Clouds and the Earth's Radiant Energy System (CERES)

“…It has been shown that regular views of the moon can be used to maintain visible radiometer stability. 11 However the fully illuminated lunar disk fills less than 10% of the CERES field of view and lunar brightness is known to vary significantly at the different phase angles when CERES lunar scans have occurred. Hence it is not currently possible to use these data as a stability metric with the precision required.…”

10. The Calibration and Characterization of Earth Remote Sensing and Environmental Monitoring Instruments

“…However, the actual comparisons of the model with the instruments include the time-dependent, cyclical changes in the lunar irradiance as viewed by the satellite instruments. Comparisons with the USGS lunar model have shown the Moon to be an exceptionally stable reference for instruments making longterm climate change measurements [250]. This has been demonstrated for measurements by individual instruments covering limited ranges of lunar phase angles [176].…”

“…Since 1993, the ROLO project at USGS in Flagstaff has acquired images of the Moon in 23 visiblehear infrared and 9 shortwave infrared bands for purposes of producing models of lunar irradiance and radiance suitable for use in calibrating and cross-calibrating satellite instruments. The ROLO lunar irradiance data has been successfully used to monitor the long term response degradation of the eight bands of the SeaWiFS instrument to 0.1 % [176,250]. Current work on ROLO is focused on reducing the 5 to 10 % absolute calibration uncertainty of the telescope systems through the determination of the system-level absolute and relative spectral response for the ROLO bands and concurrent examination of the ROLO data reduction, atmospheric correction, and modeling software [25 I].…”