1. USGS - California Fire Response -Hyperspectral Remote Sensing
Collection of airborne hyperspectral data (HyMap sensor)
Conversion to reflectance using Radiative Transfer Ground Calibration (RTGC) method
Spectral analysis to characterize and map ash and ash chemistry
Spectral Characteristics
of HyMap
Spectral Range: ~ nm
Spectral Sampling: ~ 15 nm (126 channels)
Spectral Bandpass: ~ 15 nm
Spatial Swath: ~ 2 km
Pixel Size: ~ 4 m
Hyperspectral remote sensing data were collected at each of the two sites. At Lefthand Creek, we contracted the HyMap sensor. At Sheldon NWR, we contracted the Probe-1 sensor. These are nearly equivalent sensors, though they are operated by independent companies.
<CLICK TO SHOW SENSOR CHARACTERISTICS>
The data from these sensors had these approximate characteristics:
The spectral range was the reflected solar region of 400 to 2500 nm, measured in 126 channels.
The swath width of each flight line was 2km, and the pixel size was 3.5 m.
<CLICK FOR REFLECTANCE CALIBRATION TEXT>
We convert the data from radiance to reflectance using the RTGC method of Clark et al., developed at the USGS. This requires field measurements of reflectance for a calibration site within the area covered by the remote sensing data.
<CLICK FOR GEO-CORRECTION TEXT>
In addition, geometric correction is applied to the data using ground control points selected using a DOQ reference base.
<CLICK FOR SPECTRAL ANALYSIS>
Following these important pre-processing steps, we reach the stage of analyzing the hyperspectral images in relation to the vegetation plot data.

2. HyMap Data Coverage Harris Fire 11/15/2007 Witch/
Poomacha Fires 11/19/2007
During Hymap collection, field calibration sites were measured with a field spectrometer.
Orange pins = Ash sampling sites.

3. Content of Hyperspectral Data
The shapes of spectral reflectance curves can be related to specific materials and chemical concentrations in materials

4. Example HyMap strip – Witch Fire

5. Results: AVIRIS Maps Ash/Charcoal Mineral/Ash Mineral-1mm Mineral-2mm
Green
Vegetation
Mineral/Ash
Mineral-1mm
Mineral-2mm
Dry Conifer
Dry & Green
Conifer
Straw matting
Ash/Charcoal
& Green grass
Now I will present the results from the AVIRIS data. The five broad categories established from an examination of the Tetracorder results were: 1) pixels with heavy cover by ash/charcoal, 2) pixels showing spectral features of minerals, indicating areas of exposed soil/rock, 3) pixels containing dry conifer, 4) pixels covered by dry straw matting, and 5) pixels with green vegetation. These can be thought of in terms of indicating the severity of the fire, with higher severity resulting in ash/charcoal cover and bare mineral soil/rock. Moderate severity has resulted in dried conifer trees. And low severity areas are revealed by the continued cover of green vegetation after the fire.

6. Ash/Charcoal Mineral/Ash Mineral-1mm Mineral-2mm Dry Conifer
Green
Vegetation
Mineral/Ash
Mineral-1mm
Mineral-2mm
Dry Conifer
Dry & Green
Conifer
Straw matting
Ash/Charcoal
& Green grass
Looking in more detail at the severely burned area in the center of the image we can see the highly variable nature of the post-fire surface cover, with most of the surface being exposed soil and rock mixed with some ash/charcoal (the blue pixels). Within this we see areas of heavy ash/charcoal deposits that obscure any mineral absorption features. The importance of this variation is that it might be revealing variations in nutrients released by the fire that are now available to plants.
The dry straw matting was detected by its match to dry grass spectra used in the Tetracorder analysis. After its detection, we found out from the Forest Service that this dry straw was placed on the surface to prevent erosion, with an added mix of seeds in the hopes of establishing green plants which would further stabilize the soil.
The next set of images shows the patterning of dry conifers along the edges of severe burns