Absolute Calibration of Optical Satellite Sensors Using Libya 4 Pseudo Invariant Calibration Site

TLDR

Satellite sensors differ in spectral bandpass width, overpass time, off‑nadir viewing capability, spatial resolution, and revisit interval. The paper reports improvements to an empirical absolute calibration model developed at South Dakota State University using the Libya 4 pseudo‑invariant calibration site. The model was constructed from Terra MODIS data, extended with EO‑1 Hyperion to cover visible and near‑infrared, and validated using a BRDF model derived from MODIS observations over Libya 4 against nadir data from Aqua MODIS, Landsat 7 ETM+, and other sensors such as UK‑2 DMC, ENVISAT MERIS, and Landsat 8 OLI. The refined calibration model, accounting for off‑nadir BRDF effects and annual atmospheric variations, achieves about 3 % accuracy with a 2 % uncertainty for the evaluated sensors.

Abstract

The objective of this paper is to report the improvements in an empirical absolute calibration model developed at South Dakota State University using Libya 4 (+28.55°, +23.39°) pseudo invariant calibration site (PICS). The approach was based on use of the Terra MODIS as the radiometer to develop an absolute calibration model for the spectral channels covered by this instrument from visible to shortwave infrared. Earth Observing One (EO-1) Hyperion, with a spectral resolution of 10 nm, was used to extend the model to cover visible and near-infrared regions. A simple Bidirectional Reflectance Distribution function (BRDF) model was generated using Terra Moderate Resolution Imaging Spectroradiometer (MODIS) observations over Libya 4 and the resulting model was validated with nadir data acquired from satellite sensors such as Aqua MODIS and Landsat 7 (L7) Enhanced Thematic Mapper (ETM+). The improvements in the absolute calibration model to account for the BRDF due to off-nadir measurements and annual variations in the atmosphere are summarized. BRDF models due to off-nadir viewing angles have been derived using the measurements from EO-1 Hyperion. In addition to L7 ETM+, measurements from other sensors such as Aqua MODIS, UK-2 Disaster Monitoring Constellation (DMC), ENVISAT Medium Resolution Imaging Spectrometer (MERIS) and Operational Land Imager (OLI) onboard Landsat 8 (L8), which was launched in February 2013, were employed to validate the model. These satellite sensors differ in terms of the width of their spectral bandpasses, overpass time, off-nadir-viewing capabilities, spatial resolution and temporal revisit time, etc. The results demonstrate that the proposed empirical calibration model has accuracy of the order of 3% with an uncertainty of about 2% for the sensors used in the study.