Dear Michelle,

The tool stores -9999 when the points are in a shapefile and when there is “no data” available at the location and date of the point. It uses -9999 because shapefiles cannot store null values; if you put the points in a geodatabase features class, null will be stored instead of -9999. You can instruct the tool to use a different value than -9999 to indicate no data, if desired (look under the Interpolation Options of the tool).

The most common reason for no data being available is that the points are in a location or time that tends to be cloudy. To check whether the tool seems to be operating correctly, you could run the Create Rasters tool in the same folder as the Interpolate tool with the same parameters (satellite, temporal resolution, etc.). Use the Spatiotemporal Extent options of the Create Rasters tool to specify the geographic bounding box and a range of dates enclosing your points. Then, after the tool has downloaded the rasters, load one into ArcMap and overlay the points within the date range covered by that raster. Then verify that the tool is extracting the values properly. Assuming that it is, then you can examine the time series of rasters to get an idea how cloudy the region is, or whether there is some other reason why data might be missing so frequently.

Note: before doing this, you should check the Interpolation Method parameter of the Interpolate tool. By default it is set to Nearest. This means that you should be able to overlay the points on the rasters in ArcMap and verify that each point has the exact value of the cell beneath it (assuming you have matched the points and rasters correctly by date). If the Interpolation Method is Linear, the tool will perform trilinear interpolation, in which the point receives the weighted average of the eight cells that surround it (four cells from each of the two images that enclose it in time). This will mean the points will not match the exact value of the cell beneath them, as the points have been given that weighted average.

Best,

Jason

From: [mailto:] On Behalf Of Michelle Valliant
Sent: Friday, August 5, 2016 2:15 PM
To:
Subject: [mget-help] extracting SST measurements from a dataset using MGet tool