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Images to Work With
Image of a satellite view of central Kenya durning the dry season.  This image links to a more detailed image.Satellite View of Central Kenya in the Dry Season Here is a Landsat view of Central Kenya. The resolution of this image is not great enough to show any dambos. However, it does show the general region of the study area, which can be seen in the upper left of the next satellite image. The study area is near two converging stream beds. Photo: Digital Imagery provided by Space Imaging EOSAT

Image of the Dambo Study Area.  This image links to a more detailed image.Image of the Dambo Study Area This Landsat Thematic Mapper (TM) image shows the dambo study area at Sukari Ranch. In this exaggerated true-color image, TM bands 3, 2, and 1 are represented by the colors red, green, and blue respectively. Right: Remote sensing image of the dambo study area. Photo: Digital Imagery provided by Space Imaging EOSAT

Band 3 (0.63-0.69 m) This band is in the red portion of the spectrum. A strong chlorophyll absorption band is located in the same portion of the spectrum. Consequently, this band is useful for discriminating between different vegetation types. The detected energy in this band is printed in this picture as the color red.

Band 2 (0.52-0.6 m) This band is in the green portion of the spectrum. The green reflectance peak of vegetation is found within the same portion of the spectrum. This band can be used to assess the health and vigor of plants. The detected energy in this band is printed in this picture as the color green.

Band 1 (0.45-0.52 m) This band is in the blue-green portion of the spectrum. Light within this spectral band penetrates deeper into water than the longer wavelength light of other Landsat spectral bands. Therefore, this band is useful for distinguishing features below the surface of water. It is also useful for distinguishing deciduous from coniferous plants, as well as for distinguishing soil from vegetation. The detected energy in this band is printed in this picture as the color blue.

Image of dambos found in ground truth observations. This image links to a more detailed image.Dambos Found by Ground Observations
An observer on the ground can identify dambos by their lush, abundant, and distinctive grasses. Their exact coordinates can then be pinpointed within a few tens of meters using the Global Positioning System (GPS), and the pattern of energy reflectivity characteristic of the grasses can be obtained with a spectroradiometer. Through these methods, eight dambos were identified, verified, and outlined in yellow on the satellite image to the left.
Left: Dambos found in Ground Truth Observations. Photo: Digital Imagery provided by Space Imaging EOSAT

Ground Truthing
Global Positioning, spectroradiometry, and aerial photography are used in ground truthing. The term ground truthing describes generation of data gathered on the ground, in the air, or under the water. The purpose of ground truth measurements is to verify the accuracy of the interpretation of remotely sensed data. For example, when using Landsat images to identify large areas of vegetation, ground truth methods can be used for spot verification. That is, a spectroradiometer can be used on-site to measure the energy reflected as a function of wavelength from several types of vegetation. At the site, the data collector can visually identify different types of vegetation and their characteristic patterns of reflectivity. These data can then be compared to the pattern of reflected energy observed in various bands used in Landsat images to verify that the interpretation ascribed to them is correct.

Images taken at wet and dry seasons. This image links to a more detailed image.Images Taken at Wet and Dry Seasons There is a substantial difference between images of the study area taken during the dry season and those taken during the wet season. The wet season causes the flooding of the dambos and the growth of more plant life throughout the region. Right: Comparison of dry and wet season images. Photo: Digital Imagery provided by Space Imaging EOSAT

Close-up Wet Season Image A close-up of the area during the wet season can help in the identification of dambos. See if you can find any areas that were identified as dambos by ground truth observations. This close-up view was taken within Landsat bands 4, 5, 1 represented as red, green, blue, respectively. These filters are used to bring out any vegetation features.

Image of a close-up view of area during the wet season. This image links to a more detailed image.Band 4 (0.76-0.9 m) This band is located in the near infrared portion of the spectrum. It measures reflected infrared radiation. It is useful for mapping shorelines and determining biomass content. The detected energy in this band is printed in this picture as the color red. Left: Close-up view of area during the wet season. Photo: Digital Imagery provided by Space Imaging EOSAT

Band 5 (1.55-1.75 m) This band is located in the middle infrared portion of the spectrum. It also measures reflected infrared radiation. The intensity of this band indicates the moisture content of the soil and the vegetation. This wavelength can penetrate thin clouds and is a useful discriminant between different vegetation types. The detected energy in this band is printed in this picture as the color green.

Band 1 (0.45-0.52 m) This band is in the blue-green portion of the spectrum. Light within this spectral band penetrates deeper into water than the longer wavelength light of other Landsat spectral bands. Therefore, this band is useful for distinguishing features below the surface of water. It is also useful for distinguishing deciduous from coniferous plants, as well as to distinguish soil from vegetation. The detected energy in this band is printed in this picture as the color blue.

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