Abstract
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.
PICS Normalization: Improved Temporal Trending Using PICS
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.