Empirical Absolute Calibration Model for Multiple Pseudo-Invariant Calibration Sites

Abstract

This work extends an empirical absolute calibration model initially developed for the Libya 4 Pseudo-Invariant Calibration Site (PICS) to five additional Saharan Desert PICS (Egypt 1, Libya 1, Niger 1, Niger 2, and Sudan 1), and demonstrates the efficacy of the resulting models at predicting sensor top-of-atmosphere (TOA) reflectance. It attempts to generate absolute calibration models for these PICS that have an accuracy and precision comparable to or better than the current Libya 4 model, with the intent of providing additional opportunities for sensor calibration. In addition, this work attempts to validate the general applicability of the model to other sites. The method uses Terra Moderate Resolution Imaging Spectroradiometer (MODIS) as the reference radiometer and Earth Observing-1 (EO-1) Hyperion image data to provide a representative hyperspectral reflectance profile of the PICS. Data from a region of interest (ROI) in an “optimal region” of 3% temporal, spatial, and spectral stability within the PICS are used for developing the model. The developed models were used to simulate observations of the Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+), Landsat 8 (L8) Operational Land Imager (OLI), Sentinel 2A (S2A) MultiSpectral Instrument (MSI) and Sentinel 2B (S2B) MultiSpectral Instrument (MSI) from their respective launch date through 2018. The models developed for the Egypt 1, Libya 1 and Sudan 1 PICS have an estimated accuracy of approximately 3% and precision of approximately 2% for the sensors used in the study, comparable to the current Libya 4 model. The models developed for the Niger 1 and Niger 2 sites are significantly less accurate with similar precision.

Hyperspectral Empirical Absolute Calibration Model Using Libya 4 Pseudo Invariant Calibration Site

“…In case of Vicarious calibration, the limited frequency of data collections had been improved by RadCalNet but it had come at the expense of field equipment at calibration sites and can be labor-intensive [8]. On the other hand, Pseudo-Invariant Calibration Sites (PICS) have been widely adopted to perform cross-calibration and monitoring sensor stability [1][2][3][4]9] overcoming the limitations of some calibration techniques.…”

“…The absolute radiometric calibration refers to converting an image into digital numbers (DN) or the recorded voltage by a satellite sensor into physical quantities. Those physical units can be of at-sensor spectral radiance (W• sr −1 • m −2 ) or apparent top of the atmosphere reflectance [1,2].…”

Vicarious Methodologies to Assess and Improve the Quality of the Optical Remote Sensing Images: A Critical Review

“…The improved Libya 4 empirical model accuracy is between 2% and 3%, and precision is between 1% and 2%. In 2019, Bipin et al extended the work presented in [33] through applying the APICS model to five other PICS [49]. The results show that the model for Egypt 1, Libya 1 and Sudan 1 PICS has approximately 2-3% accuracy and 1-2% precision.…”

“…The APICS model, described in [33,49] by Mishra et al and Bipin et al, was developed using Terra MODIS and Hyperion observations of PICS. Terra MODIS was selected as a source for absolute calibration because it is one of the best-calibrated sensors, with 2% uncertainty in Top-of-Atmosphere (TOA) reflectance scale [51], and the Hyperion hyperspectral sensor was used as a source of hyperspectral profile due to its 3-5% accuracy and around 2% repeatability (prior to 2012 data) [52,53].…”

“…An empirical BRDF model for solar zenith angle was developed using nadir-looking Terra MODIS observations. As explained in [49], to account for the varying view zenith angle, a view zenith BRDF model was developed from a spectrally cleaner (high transmittance and reflectance) Hyperion band.…”