Sentinel-2: ESA's Optical High-Resolution Mission for GMES Operational Services

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.

/pdf/the-spectral-irradiance-of-the-moon-4m46f9p1xs.pdf

The Spectral Irradiance of the Moon

Absolute radiometric calibration of Landsat 7 ETM+ using the reflectance-based method

Low resolution satellite imagery has been extensively used for crop monitoring and yield forecasting for over 30 years and plays an important role in a growing number of operational systems. The combination of their high temporal frequency with their extended geographical coverage generally associated with low costs per area unit makes these images a convenient choice at both national and regional scales. Several qualitative and quantitative approaches can be clearly distinguished, going from the use of low resolution satellite imagery as the main predictor of final crop yield to complex crop growth models where remote sensing-derived indicators play different roles, depending on the nature of the model and on the availability of data measured on the ground. Vegetation performance anomaly detection with low resolution images continues to be a fundamental component of early warning and drought monitoring systems at the regional scale. For applications at more detailed scales, the limitations created by the mixed nature of low resolution pixels are being progressively reduced by the higher resolution offered by new sensors, while the continuity of existing systems remains crucial for ensuring the

Using Low Resolution Satellite Imagery for Yield Prediction and Yield Anomaly Detection

https://laketahoe.jpl.nasa.gov/publications/2001_hook_modis_aster_airborne.pdf

The MODIS/ASTER airborne simulator (MASTER) - a new instrument for earth science studies

Since their launch in February 1986 and January 1990, we have, from time to time, conducted radiometric calibrations of the SPOT-1 and -2 Haute Resolution Visible (HRV) cameras at White Sands, New Mexico. We summarize the results of the calibrations, comparing the absolute calibration coefficients obtained from the White Sands data to the relative calibrations obtained from the on-board tungsten lamp.

Review of SPOT-1 and -2 calibrations at White Sands from launch to the present

Three methods for determining an absolute radiometric calibration of a spacecraft optical sensor are compared. They are the well-known reflectance-based and radiance-based methods and a new method based on measurements of the ratio of diffuse-to-global irradiance at the ground. The latter will be described in detail and the comparison of the three approaches will be made with reference to the SPOT-2 HRV cameras for a field campaign 1990-06-19 through 1990-06-24 at the White Sands Missile Range in New Mexico.

Radiometric calibration of SPOT 2 HRV: a comparison of three methods

The present study is part of an investigation aimed at optimizing the use of desertic sites for absolute or relative calibration of satellite visible sensors. This effort includes characterization of the surface, gathering of climatology or atmospheric data sets, ground- and air- based measurements as well as result of calibration of various sensors over these sites. All these measurements and estimates are stored in a repository and made available to various methods for calibration. Post-launch degradation and relative sensitivity of various sensor have been estimated using north african desertic sites as radiometrically stable targets. The selected area have first been characterize in terms of bidirectional and spectral reflectances by making use of POLDER capabilities, then to cross-calibrate SeaWifs, VEGETATION on-board SPOT4 and AVHRR on-board NOAA-14 by reference to POLDER. Results are compared with absolute and relative calibration issued from other sources. Extensive period of time are spanned to assess the ability of this method to monitor long term trends in sensor evolutions. Results of this cross calibration will be presented. The method developed for this study will be presented as well, in order to make it applicable to other sensor. A sensitivity study has also been realized, considering synthetic data, allowing to evalute the main contributions to the error budget. The need for aerosol optical thickness is then evidenced, and will lead to the set up of a sun photometer on one of the selected sites in 1999.

Remote sensing data respository for in-flight calibration of optical sensors over terrestrial targets

SPOT absolute and multitemporal calibration is achieved using the on-board lamp plus regular checks over White Sands or other test sites which radiance is derived from ground measurements during the satellite overpass. In order to develop another independent method to monitor the long term evolution of the cameras sensitivity, systematic acquisitions of stable desert areas have been decided. The choice of the sites have been made based upon stability studies on images of large field of view satellites (METEOSAT and AVHRR). We now dispose of more than two years of systematic SPOT2 observations over three north Africa areas for all the modes of the two cameras, plus some SPOT1 acquisitions. For the time being, only four sites have been processed (acquired in (Chi) s mode by the HRV1 camera). The first results are promising and show: (1) a good stability of the sites (specially in (Chi) s2), (2) a good agreement with the on-board lamp, (3) a good consistency between SPOT1 and SPOT2 calibration.

SPOT multitemporal calibration over stable desert areas

The Rayleigh scattering over a clear ocean is a target which radiance is very well modeled and which enables to calibrate the short wavelengths of remote sensing instruments. But the quality of the calibration strongly depends on the evaluation of the other contributors to the observed Top Of Atmosphere radiance i. e. aerosol scattering and reflection over the sea surface (water color, foam, glint...). However these contributors can be reduced by appropriate viewing conditions. This technique is used to calibrate B1 (051-0.59 µm) and B2 (0.61-0.68µm) channels of HRVIR camera, and B0 (0.4-0.5µm) and B2 channels of VEGETATION camera both of which are aboard SPOT4. This article presents the calibration results obtained during the satellite two years in orbit. The results are compared to: - pre-flight results (integrating sphere) - in-flight results. The in-flight results are provided by: - on board calibration system (lamp and sun sensor) - vicarious calibration over test sites (White Sands, La Crau) - calibration over stable deserts - calibration over the sun glint The analysis of the sensitivity of the calibration to the different parameters used to model the TOA radiance shows the accuracy of such a technique.

Patrice Henry

Papers

Review of SPOT-1 and -2 calibrations at White Sands from launch to the present

Radiometric calibration of SPOT 2 HRV: a comparison of three methods

Remote sensing data respository for in-flight calibration of optical sensors over terrestrial targets

SPOT multitemporal calibration over stable desert areas

Calibration of SPOT4 HRVIR and Vegetation cameras over Rayleigh scattering