Part II of SMAP Scientist Blog: How do SMAP Scientists Use GLOBE Data?

How do SMAP Scientists Use GLOBE Data (Part II)?

Data Analysis and Blog by Dr. Erika Podest, SMAP Scientist

In order to start using GLOBE soil moisture data we need at least 15 measurements collected on days when SMAP flew overhead. The Varazdin School is an example of such and the chart below is a comparison between their data and SMAP soil moisture at 36 km2 spatial resolution.

Figure 2: Comparison between SMAP and GLOBE soil moisture from Varazdin school in Croatia.

There are several things to note in Fig. 2. First, GLOBE measurements collected early on did not match those of SMAP because there was either snow or ice on the ground or the soil was frozen. Under such conditions SMAP cannot measure soil moisture well, which is why the trends do not correlate. For this reason it is very important that you note the conditions on the ground. Second, once the thaw period began, from around mid May through late October, the soil moisture trends (wetting and drying) matched very well. Finally, because the GLOBE measurement is just one point on the ground while the SMAP measurement covers an area of approximately 36 km2, we do not expect to see a close match in the values but rather a close match in the trend of changing soil moisture with time.

The SMAP data currently being distributed is not yet fully validated and is considered a beta version. We will post the fully validated data around the end of April onwards. Your measurements are therefore of great value to help support this critical part of the SMAP satellite mission. We thank all the schools that with such great enthusiasm have and continue to collect soil moisture measurements in support of SMAP.

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