PICS Normalization: Improved Temporal Trending Using PICS
Dennis L. Helder, Harika Vuppula, Leah Ervin, Ruchira Tabassum, Morakot Kaewmanee · Digital Commons - USU (Utah State University) · 2016
Pseudo Invariant Calibration sites (PICS) have been used as a method of vicarious calibration of optical remote sensing satellites since the turn of the century. The broadest application comes from trending satellite responsivity and cross-calibration of satellites, although some have suggested that absolute radiometric calibration using PICS is also possible. Trending of satellite responsivity is done simply by imaging a PICS with the satellite sensor as often as possible over a period of time. If the PICS is truly invariant, then any trend in the data would indicate a change in sensor responsivity rather than a change in the apparent reflectance of the target/atmosphere system. However, the length of time that is required to determine a change in sensor responsivity is a function of the residual noise in the PICS target/atmosphere system and the number of days between imaging opportunities with the sensor being calibrated. Often this can require several years of imaging PICS to detect a small change in sensor responsivity. This paper presents an augmented PICS calibration approach that seeks to combine sensor observations of multiple PICS into a single time series with greater temporal resolution. Six primary Saharan PICS locations were identified according to their level of temporal/spatial stability. Each of these sites was normalized to the well-known Libya 4 PICS which is used as the overall reference calibration site. As a result, the temporal resolution using this method can theoretically be improved by a factor of six. This technique was applied to Landsat data to determine if small changes in sensor responsivity can be detector in a shorter time period than when only one PICS is utilized in the trending process. Results showing the effect of greater temporal resolution on PICS trending precision will be presented.