| Autor: |
Harris, Norman, Johnson, D. E., Righetti, T. L., Barrington, M. R. |
| Zdroj: |
Geocarto International; September 1996, Vol. 11 Issue: 3 p99-104, 6p |
| Abstrakt: |
Measurement of rangeland vegetation is time consuming, tedious and expensive. Any method that can accurately measure and spatially ordinate vegetation more quickly or cheaply, is welcomed by range professionals. We have used blimp borne cameras to document and monitor range vegetation for several years. A tethered 5.5 m helium filled blimp is used to lift a photographic platform to altitudes from several to a maximum of 150 m. The blimp is used to photograph plots from a stationary position or pulled across a landscape to obtain images along a transect. The frame holding the sensor platform is gimbaled to ensure that cameras maintain a vertical orientation. Radio-controlled servos are used to rotate the platform and to trigger paired self-advancing cameras. Paired photos obtained using color and infrared film can then be examined directly or via computer processing. Photographs are processed into slides and converted to digital images on compact disk. If a Global Positioning System (GPS) is used to locate ground features, images can be geocorrected and rectified. Paired images contain four bands of data: red, green, blue, and infrared. Picture elements (pixels) obtained using a 28mm f/2.8 wide angle lens are approximately 1.5 cm2 at an altitude of 25 meters and 25 cm2 at 100 m. Digital image processing facilitates enhancement of spectral differences between soil and vegetation and calculation of percent cover for plants. Information is easily stored and retrieved in digital format. Photographs and classified digital images have been very useful for monitoring reference areas, critical sites, or changes on rangelands. Blimp technology can be used with videography and digital cameras which should speed the processing of data. |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
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