Ryan S.

6/11/99

Earth/Space
Period 4

Satellite Imagery Test #2 Part A

Remote sensing is gathering and sorting information from a distance. The tools we use to do this are satellites and we gather the information from space. From space we see our world in a whole new perspective which gives us information about the activity on our Earth and life on our planet. We can see the "Big Picture" now and we have the power to learn more and understand our planet.

In the video, we learned about a global problem known as deforestation, which is occurring in rainforests around the world. Farmers who were clearing farmland were destroying many rainforests. By using satellites, scientists could see where various fires were taking place where farmers were clearing land. Also, the area where the vegetation was gone could be picked up. Samples from dead trees were taken to get some of the sulfur dioxide out. Then they were used for satellites so that they could now sense where the vegetation was dying of acid rain.

This is a graph of a spectral signature chart. What this graph shows is how much light reflectance a certain substance gives off when one form of light is reflected off of it. The different forms of light are shown on the horizontal axis and the wavelength in centimeters is also shown, indicating the wavelength the reflected light has. The percent reflectance is shown on the vertical axis, indicating what percentage of the light is reflected off the object.

On a digital image, you would want certain features to stand out that you want to view the most. Therefore, for those features you would select the bandwidth that provides the most reflectance for that surface. Also, you would choose the form of light (i.e. microwave, infrared, etc.) that provides the most reflectance. You could use this graph to decide which bandwidth would be best to view that feature of the image because the graph shows which wavelength and light form provides the most reflectance for that object.

Three Steps:

1. First, bandwidths must be selected. TM and MSS images are made using infrared

2. Secondly, the infrared light that is picked up by the TM and MSS bands must be turned into binary code and sent down to Earth using radio waves. There is will be picked up by a satellite dish and sent to a computer.
3. Thirdly, the false color should be selected. The colors that are selected will also help certain desired features stand out in the image.

Radar imaging is the use of satellites to create digital images using radar waves, or microwaves. The reason this is an active system is because the satellite sends out the radar waves instead of just receiving them. When the radar hits a surface, it sends backscatter in all directions, which is then picked up by the satellite.

First of all, the satellite sends out radar waves, which hit the surfaces on the Earth and bounce back as backscatter. When the satellite picks them up again, they go through polarized lenses, which only let certain light through depending on the lenses (HH, VV, or HV). Then the satellite determines the dB values of the information received by using the polarization. The dB value will be high or low (-5 to ö20) depending on the amount of backscatter. The information is then sent to Earth in binary code using radio waves and is picked up by a satellite dish, which transfers the information to a computer. Using the information the image is created and false color is added in.

One reason radar imaging is used is to view topographic features like mountains and volcanoes. Another is as a device for seeing through clouds so the images with and without clouds could be compared. A third is for changes in land structures by seeing the amount of backscatter given off for a certain area. Radar imaging is ideal for viewing topographic features and viewing Earth through the clouds.

When the satellite picks up the radar backscatter, the light goes through a certain combination of polarized lenses (HH, VV, or HV) which can vary and create different false color images. Then the polarized lenses pick up the dB values. The information is sent to a satellite dish and a computer on Earth using radio waves and binary code, and the polarization and dB values are interpreted into a false color image.

8A. Explain what backscatter is.

Backscatter is the amount of reflectance off of an object that radar waves have when they bounce off an object. Backscatter can come from any direction and usually is determined by the angle of incidence that it hits the object or the roughness of an object. Double bounces can also occur where the waves bounce off two objects.

Urban, agriculture and forested regions all have different amounts of backscatter that are reflected when radar waves hit them. Urban areas have backscatter higher than ö5dB, agricultural areas are from ö20 to ö10dB, and forested areas are below ö20dB (-5=high; -20=low). Over a ten-year period, areas that had relatively high backscatter could have dropped to a lower amount (i.e. forests got chopped down to use the land for farming) or low backscatter could have changed to high (i.e. a burnt down forest grew back). Using the dB values, scientists could study changes in land areas by seeing vegetation growth or depletion and even the construction of man-made structures.