Radiometric calibration stability and inter-calibration of solar-band instruments in orbit using the moon

Abstract

With the increased emphasis on monitoring the Earth's climate from space, more stringent calibration requirements are being placed on the data products from remote sensing satellite instruments. Among these are stability over decade-length time scales and consistency across sensors and platforms. For radiometer instruments in the solar reflectance wavelength range (visible to shortwave infrared), maintaining calibration on orbit is difficult due to the lack of absolute radiometric standards suitable for flight use. The Moon presents a luminous source that can be viewed by all instruments in Earth orbit. Considered as a solar diffuser, the lunar surface is exceedingly stable. The chief difficulty with using the Moon is the strong variations in the Moon's brightness with illumination and viewing geometry. This mandates the use of a photometric model to compare lunar observations, either over time by the same instrument or between instruments. The U.S. Geological Survey in Flagstaff, Arizona, under NASA sponsorship, has developed a model for the lunar spectral irradiance that explicitly accounts for the effects of phase, the lunar librations, and the lunar surface reflectance properties. The model predicts variations in the Moon's brightness with precision ∼1% over a continuous phase range from eclipse to the quarter lunar phases. Given a time series of Moon observations taken by an instrument, the geometric prediction capability of the lunar irradiance model enables sensor calibration stability with sub-percent per year precision. Cross-calibration of instruments with similar passbands can be achieved with precision comparable to the model precision. Although the Moon observations used for intercomparison can be widely separated in phase angle and/or time, SeaWiFS and MODIS have acquired lunar views closely spaced in time. These data provide an example to assess inter-calibration biases between these two instruments.

Updated inflight calibration of Hayabusa2's optical navigation camera (ONC) for scientific observations during the cruise phase

“…The relative uncertainty is based on the ROLO model comparison with lunar brightness measurements taken with Moderate Resolution Imaging Spectroradiometer, which is a well calibrated Earth observing sensor onboard Aqua and Terra (Stone, 2008). Thus, the updated sensitivity reproduces the lunar radiance spectrum to within the ambiguity in the models.…”

On-orbit calibration of SeaWiFS

“…Over this time, the US Geological Survey has developed the RObotic Lunar Observatory (ROLO) photometric model of the Moon to provide geometric corrections for on-orbit lunar observations obtained by remote sensing satellite instruments over the wavelength range of 300-2500 nm [8][9][10]. The model explicitly accounts for the effects of Sun-Moon and instrument-Moon distances and for the effects of phase and libration angles of the lunar observations.…”

VIIRS day/night band radiometric calibration stability monitoring using the Moon

“…The absolute uncertainty of the ROLO model prediction can be as large as 5–10% for the short‐wavelength bands and even larger for the NIR bands. However, for a given spectral band, the stability of the irradiance predicted by the ROLO model over a limited range of lunar phase angles and libration angles is much smaller [ Stone , ]. Since the lunar phase angle is confined within a limited range, the relative uncertainty of the lunar irradiance predicted by the ROLO model for VIIRS scheduled lunar observations is expected to be about 1%.…”