Using satellite data to detect differences in soil moisture

April 24th, 2009 |
GOES-12 visible images

GOES-12 visible images

GOES-12 visible images (above) showed that much of Iowa and northern Illinois were cloud-free during the morning and early afternoon hours on 24 April 2009. There appeared to be some subtle differences in the soil types over parts of those regions, with some areas exhibiting a slightly darker appearance on the visible imagery.

However, GOES-12 3.9 µm shortwave IR images (below) indicated the presence of a broad swath of notably cooler ground, oriented SW-NE across northern Illinois — this was due to moist soils from significant rainfall during the overnight hours (radar-estimated Storm Total Precipitation). Surface air temperatures appeared to be responding a bit more slowly to the daytime solar heating over the swath of cooler wet ground that was seen on the IR imagery.

GOES-12 3.9 µm shortwave IR images

GOES-12 3.9 µm shortwave IR images

AWIPS images  of the MODIS visible channel, 3.7 µm shortwave IR channel, and Land Surface temperature (LST) product (below) also showed a higher-resolution view of the swath of cooler ground  — the LST values over the swath of wet ground were generally in the upper 70s F (orange colors), compared to the upper 80s F (red colors) over the adjacent dry ground areas. Also note the very high LST values of 100-110º F (darker red colors) over parts of western Iowa — these high LST values corresponded to freshly plowed fields where newly-planted crops had not yet begun to come up.

MODIS visible, 3.7 µm shortwave IR, Land Surface Temperature images

MODIS visible, 3.7 µm shortwave IR, Land Surface Temperature images

Over Iowa, note how the MODIS Normalized Difference Vegetation Index (NDVI) values were lower (0.2 to 0.3) in areas where the Land Surface Temperature (LST) values was the highest (below). The MODIS NDVI values were similar over much of northern Illinois, but due to the wet condition of the soil the LST values were much lower in that region.

MODIS LST product + NDVI product

MODIS LST product + NDVI product

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