Abstract
A lunar observation campaign was conducted using a hyper-spectral imaging spectrometer in Lijiang, China from December 2015 to February 2016. The lunar hyper-spectral images in the visible to near-infrared region (VNIR) have been obtained in different lunar phases with absolute scale established by the National Institute of Metrology (NIM), China using the lamp–plate calibration system. At the same time, the aerosol optical depth (AOD) is measured regularly by a lidar and a lunar CE318U for atmospheric characterization to provide nightly atmosphere extinction correction of lunar observations. This paper addressed the complicated data processing procedure in detail from raw images of the spectrometer into the spectral lunar irradiance in different lunar phases. The result of measurement shows that the imaging spectrometer can provide lunar irradiance with uncertainties less than 3.30% except for absorption bands. Except for strong atmosphere absorption region, the mean spectral irradiance difference between the measured irradiance and the ROLO (Robotic Lunar Observatory) model is 8.6 ± 2% over the course of the lunar observation mission. The ROLO model performs more reliable to clarify absolute and relative accuracy of lunar irradiance than that of the MT2009 model in different Sun–Moon–Earth geometry. The spectral ratio analysis of lunar irradiance shows that band-to-band variability in the ROLO model is consistent within 2%, and the consistency of the models in the lunar phase and spectrum is well analyzed and evaluated from phase dependence and phase reddening analysis respectively.
Highlights
A standard reference source using the Moon is established to provide on-orbit stable and accurate radiometric calibration in solar reflective wavelength range (350–2500 nm) [1], and detect against small systematic drifts in the radiometric response of instruments over many years [2,3]
The most frequently used photometric model is reported by the Robotic Lunar Observatory (ROLO) project [10,26], and this lunar model is based on an extensive database of radiance images acquired by the United States Geological Survey
To validate the current lunar models, a 3-month observing campaign spanning a wide range of lunar phase has been performed from Lijiang observatory in the visible to near-infrared region (VNIR)
Summary
A standard reference source using the Moon is established to provide on-orbit stable and accurate radiometric calibration in solar reflective wavelength range (350–2500 nm) [1], and detect against small systematic drifts in the radiometric response of instruments over many years [2,3]. A long-term set of lunar observations and cross calibration [5] are put forward by future missions such as CLARREO and TRUTHS [6], and the Moon has gradually become the first choice of an absolute celestial target for multiple sensors [7]. The most careful radiometric study of the Moon to date is reported by the Robotic Lunar Observatory (ROLO) project, and this lunar model [10]—based on the extensive database of radiance images—has been developed to support radiometric calibration of Earth-view spacecraft instruments. As a relative on-orbit target, the tendency of the lunar model with lunar phase cannot satisfy current requirements for cross calibration between different phase angles [11].
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