The Spectral Irradiance of the Moon

Abstract

Images of the Moon at 32 wavelengths from 350 to 2450 nm have been obtained from a dedicated observatory during the bright half of each month over a period of several years. The ultimate goal is to develop a spectral radiance model of the Moon with an angular resolution and radiometric accuracy appropriate for calibration of Earth-orbiting spacecraft. An empirical model of irradiance has been developed that treats phase and libration explicitly, with absolute scale founded on the spectra of the star Vega and returned Apollo samples. A selected set of 190 standard stars are observed regularly to provide nightly extinction correction and long-term calibration of the observations. The extinction model is wavelength-coupled and based on the absorption coefficients of a number of gases and aerosols. The empirical irradiance model has the same form at each wavelength, with 18 coefficients, eight of which are constant across wavelength, for a total of 328 coefficients. Over 1000 lunar observations are fitted at each wavelength; the average residual is less than 1%. The irradiance model is actively being used in lunar calibration of several spacecraft instruments and can track sensor response changes at the 0.1% level.

The wavelength dependence of the lunar phase curve as seen by the Lunar Reconnaissance Orbiter wide‐angle camera

“…The analysis of this paper requires the absolute reflectance, which is notoriously difficult to measure because of the possibility of systematic errors. In-flight calibrations in the visible are being done using Earth-based telescopic data, primarily the high-quality Robotic Lunar Observatory (ROLO) data set [Kieffer and Stone, 2005]. Unfortunately, there are few measurements of absolute lunar reflectance in the UV, and observations by the Hubble Space Telescope [Robinson et al, 2007] are being used for short-wavelength in-flight calibration.…”

Assessment of nocturnal aerosol optical depth from lunar photometry at the Izaña high mountain observatory

“…Robotic Lunar Observatory (ROLO) model, developed as a part of the USGS-and NASA-funded program for spaceborne calibration, is considered an accurate tool for exoatmospheric lunar spectral irradiance (I 0 ) estimation for a given position of the observer on the Earth's surface and at a given time (Kieffer and Stone, 2005). This empirically based model provides the Moon's irradiance at 32 wavelengths, with an uncertainty between 5 and 10 % in the absolute scale, using only geometrical variables: the absolute phase angle, the selenographic latitude and longitude of the observer, and the selenographic longitude of the Sun.…”

“…In this respect, the Robotic Lunar Observatory (ROLO) model, developed by Kieffer and Stone (2005), is the most careful radiometric study on the Moon's brightness to date (Cramer et al, 2013). The ROLO model has recently emerged as a unique tool for Moon photometry (Berkoff et al, 2011;Barreto et al, 2013aBarreto et al, , b, 2016 and is an essential part of the calibration process.…”

Auroral meridian scanning photometer calibration using Jupiter

“…Despite this substantial decrease, the equivalent brightness of nearly 10 megaRayleighs per nanometer (Table 2) is still a hundred times brighter than the brightest aurora. For many instruments the angular size of the moon is neither point-like nor beam-filling, requiring careful attention to details such as wavelength-dependent albedo varying across the disk (Kieffer and Stone, 2005), and making phase calculations more complicated. For these reasons, the moon is not commonly used for calibrating auroral instruments.…”