The core of deep convective clouds (DCC) is one of the most consistent Earth targets. When viewed from space, the measurements have minimal impact from water vapor and aerosols and have been used as invariant scenes for calibration assessment for reflectance solar bands. DCC is also one of the coldest targets and can be used for assessing the calibration and product stability for infrared thermal emissive bands (TEB). The stability from the years 2003 to 2019 is analyzed for both Terra and Aqua moderate resolution imaging spectroradiometer (MODIS) long-wave infrared bands. Most bands exhibit very stable long-term trending. Terra band 30 shows the largest rate of change of 0.19  K  /  year. The Terra–Aqua difference is also analyzed. In general, for both Terra and Aqua, the long-wave infrared bands show good and stable detector uniformity. The impact of response change due to anomalies and events has been analyzed. Since the measurement bias over cold DCC is dominated by the offset term in the calibration equation, an assessment model is developed to estimate the offset bias between the mirror sides. The impact model is also developed to estimate the impact on higher brightness temperature measurements. The offset bias from the assessment modeling in this analysis is used as the input for impact modeling. The measurements over Dome-C, Ocean, and desert scenes are used to verify the impact model. These assessments are very helpful for MODIS TEB calibration and look-up table update procedure improvements.

Meteorological Operational (METOP)-B spacecraft was launched on September 17, 2012, and the Advanced Very High Resolution Radiometer (AVHRR) visible and near-infrared channels were activated shortly after the launch. Due to the lack of on-board calibrator, the postlaunch calibration update can only be carried out vicariously. Libyan Desert reflectance with seasonal variation consideration has been used as reference since 1995. The initial updates of the calibration are derived using the seasonal oscillations of previous AVHRR measurements. In this paper, this approach is improved using the seasonal curve regression for the MetOp-B AVHRR measurement over Libyan Desert.

A new method is developed using the MetOp-A and MetOp-B inter-comparison with consideration of the Bidirectional Reflectance Distribution Function (BRDF) effect, and applied to the calibration update. Since these two satellites are in the same orbit with half orbit time (~50min) apart, it is feasible to use the inter-comparison of the AVHRR measurement on Libyan Desert between these two instruments. The solar zenith angle and sensor zenith angle are not the same for the collocated measurements, and the BRDF effects on the comparison should be corrected. The zenith angle dependent measurements have been modeled and the comparison of the reflectance with the same solar zenith angle and sensor zenith angle has been derived. The calibrations from these two methods are consistent and the updates are delivered for operational L1B product. This work is also useful to investigate BRDF effect on the inter-comparison for visible and near infrared sensors.