Fire on the Beach

April 24th, 2009 |

Fires in coastal northeastern South Carolina, (news links here and here, for example) near Myrtle Beach, have destroyed 70+ houses and forced residents to evacuate. A true-color MODIS image that shows the distinct smoke plume is available here.

The fires were visible from satellite in both the visible channels, as shown above, and in the near-infrared channels. MODIS imagery in the 3.7-micron channel shows hot spots where the peat and brush fires are active. The character of the radiation emitted by the fire is a function of the temperature, as described by Wien’s Law, with higher emitting temperatures leading to shorter wavelength emissions (as described graphically by this applet. Note in the applet how the wavelength of the peak emitted radiation decreases as the temperature increases; a fire burning with a temperature of 700-800 F will have peak emissions near 3.9 microns).

The near-infrared channel (3.9 microns) on the GOES imager is more sensitive to fire detection than the far-infrared channel (10.7 microns) in part because of the great increase in near-infrared emission that occurs as fires develop and mature. In the loop of GOES Imager information above (Visible, 10.7 micron and 3.9 micron, respectively), note the very dark (warm) pixels in the 3.9 micron image in the region of the fire. The warmest pixels have brightness temperatures of 318.5 K at 3.9 micron vs. 300 K at 10.7 microns. In comparison, both sensors have brightness temperatures of 290 K in the waters off the coast. The difference at hot temperatures arises from the enhanced 3.9 micron emissions due to the fires.

Fires are routinely monitored at CIMSS using GOES Imager data, principally visible data and the 3.9 and 10.7 micron channels. See this link for more information. The processed data for 1545 UTC on 23 April do indicated fires (red pixels) near Myrtle Beach (the color key is available here).

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