Validation Service

For functional reasons satellite and comparison measurements in general do not correspond precisely in time and space (so called mistime and misdistance). Since dynamical effects in the atmosphere lead to temporal and spatial variability of atmospheric parameters such as temperature or ozone, a non-zero mistime or misdistance can cause differences between satellite-based and validation measurements (so called mistime and misdistance error, generally addressed as mismatch error). These differences cannot be taken as a hint for the satellite instrument failure. Additionally, deviations in measurement data that are caused by differing measurement geometry of the instruments have to be taken into account (misintegration error). A typical example for such a comparison is shown in Figure 1: the black line depicts a radiosonde-based temperature measurement, the red line refers to a TIMED/SABER-based measurement. The structures are similar but not identical, the absolute values also differ to some extent. These differences might at least be in parts due to the differing measuring times and geographical coordinates (see Figure 2).

 


Figure 1: The black line depicts a radiosonde-based temperature measurement, the red line refers to a TIMED/SABER-based measurement. The structures are similar but not identical, the absolute values also differ to some extent.

Figure 2: The geographical position of the two measurements compared in Figure 1 differs by about 300km (misdistance); furthermore, the instruments did not measure at the same time (mistime). These differences are probably at least in parts responsible for the differing temperatures shown in Figure 1.

 

Analysis and quantification of the impact of natural atmospheric variability on validation is analysed and quantified as part of the project SatVal-A. The calculations are based on ERA40-data covering more than 20 years. Via our internet tool we offer this information also to you. Just enter time and geographical coordinates of two temperature measurements you would like to compare in our internet form. Based on mistime and misdistance which the program calculates for you, you receive information about the averaged mismatch error (dark blue line in Figure 3) and also about its standard deviation (light blue shaded part in Figure 3).

 

►Run SatVal-A-Tool

 

Figure 3: The dark blue line shows the averaged temperature differences calculated for the above mentioned mistime and misdistance. The values are based on ERA40-data available on a 2.5°x2.5° grid. The temperature differences are averaged over one month and more than 20 years. The light blue shaded area refers to standard deviation.