Early mission changes to the Terra satellite and their effect on MISR time series of cloud height anomalies

The Terra satellite is now in its 15th year of operation, with the various instruments on board yielding generally very homogeneously measured time series of clouds and radiation. However, there were subtle differences in the spacecraft operation in the first 2-3 years compared to the rest of the mission that are worth considering, especially since surface temperature anomalies were coincidentally greater at the start of the Terra mission compared with those in recent years.

The two main effects examined here due to differences in Terra's operations are the greater frequency of drag makeup maneuvers, resulting in reduced sampling by MISR's high resolution radiometers, and the shift in equatorial crossing time (about 15 minutes) affecting the location of sun glint patterns. The reduced sampling did not occur randomly, but favoured some orbital paths over others (an "office hours effect”), and the sun glint patterns shifted location by up to 4° in longitude, affecting the eastern edge of the swath, only for some latitudes and seasons.

By resampling the data at high resolution, these potential artifacts in the overall time series can be removed, and results compared with not taking them into account. This is done mainly in the context of obtaining homogeneous time series anomalies of effective cloud height using stereo retrievals from MISR's near nadir cameras, with relevance to detecting any long term changes in the cloud greenhouse effect.