Impacts of Temporal and Spatial Mismatch between Radiosonde Launch and Satellite Overpass on the Accuracy Assessment of Satellite Retrievals: Daily vs. Weekly vs. Monthly Scales

Radiosonde balloons and satellite soundings are not perfectly collocated when radiosonde measurements are used to calibrate or validate satellite data. For most of the radiosonde and polar satellite sounding collocations, the distance mismatch is in the range of 10 km to 90 km, and the time mismatch is in the range of 20 min to 6 hr. Does the collocation mismatch lower the “accuracy” or “performance” of satellite soundings when they are evaluated by radiosonde data? Does the mismatch impact the detection of long-term climate trend using satellite observations if calibrated by collocated radiosondes? These issues are also the concerns in the development of the GCOS Reference Upper-Air Network which is designed to provide long-term high-quality climate records and use them to constrain, adjust, and ensure satellite measurements can be used for climate purpose.

Using 2-yr collocation data generated from NESDIS's Center for Satellite Applications and Research (STAR)-operated NOAA Products Validation System (NPROVS), our analysis (the relevant paper is submitted to Geophysical Research Letter for publication) indicates that the collocation mismatch does not appear to cause an impact on the mean satellite-minus-radiosonde difference but it impacts significantly the RMS difference computed directly from daily synoptic data.

Climate trend detection could be impacted if the satellite-minus-RAOB standard deviation calculated using monthly data changes significantly with the change in distance and time mismatch even the satellite-minus-RAOB monthly mean different remains unchanged.

In this study, the mismatch impact will be examined on daily, weekly and monthly time-scales by using NPROVS collocation data. Results from the study may provide considerations needed for satellite calibration/validation of different time scales.