In-Orbit Health and Performance of Operational AVHRR Instruments

The Advanced Very High Resolution Radiometer (AVHRR) instruments on board NOAA-18, MetOp-A and NOAA-19 satellites are key components of the current operational NOAA-EUMETSAT Initial Joint Polar System (IJPS) and are routinely monitored. Overall, the results of trending analysis show that the AVHRR instruments on NOAA-18/19 and MetOp-A are functioning well outperforming the channel noise specification limits. The backup NOAA-17 AVHRR functioned well for the on-orbit period prior to the onset of scan motor failure around April 11, 2010. The sun-earth-satellite geometry driven seasonality is exhibited by temperature measurements from thermistors on various instrument housing components including blackbody with the exception of patch temperature which is typically maintained stable. The only electrical measurement which exhibits seasonality is patch power. It is shown that the seasonality has no significant adverse impact on AVHRR radiometric performance. On the other hand the space view is adversely affected by intermittent periodic lunar signals and ubiquitous low frequency variability presumably connected to space clamping mechanism. Based on this it is suggested that the AVHRR channel noise estimation should be based on blackbody view. Finally, the temporal stability of the monitored parameters and the smaller or comparable magnitudes of seasonal variability in most of the instrument housekeeping measurements as compared to their orbital variability confirm th