Remote Sensing

Question 1

What are the advantages of remote sensing for data gathering?

Answer 1

1. Quick, large area coverage is possible
2. Good geometric accuracy is possible for positioning objects
3. Detection of non-visible objects possible using films, scanners and filters
4. Instantaneous record when taken, and historical records kept easily

Question 2

What are some platforms used for remote sensing?

Answer 2

Balloons, planes, satellites

Question 3

What is the aerial photo scale computation formula?

Answer 3

f = focal length of lens
a = altitude 

scale = f/a

Slide 5

Question 4

Why does scale distortion occur in aerial photography?

Answer 4

If features on the image are at different distances from the lens when the photo is taken, they are at different scales.

Question 5

What is terrain displacement?

Answer 5

1) Features at higher elevations are closer to the lens.
2) They are at larger scales.
3) Larger scales make features appear larger on the photo, and displace them in position

Question 6

Smaller scale = ____ detail

Larger scale = ______ detail

Answer 6

Less

More

Question 7

What are the advantages of satellite platforms and scanners over aerial platforms?

Answer 7

Reduced effect of terrain displacement at very high altitude.

Stability of Platforms

Question 8

What is LANDSAT?

Answer 8

An earth observation sensor that makes thematic maps.

Question 9

What are some attributes of LANDSAT?

Answer 9

1) 7 spectral bands
2) 30 meter resolution
3) repeat coverage of 16 days
4) broad coverage per scene with images of 185km on a side (13,207 square miles)
5) Data back to 1972 with Landsat 1

Question 10

What are passive vs active sensors?

Answer 10

Passive sensors that record reflected light are limited to daytime (or thermal bands) and to clear skies. Active sensors can emit their own signals and record reflectivity. (e.g. The Canadian RADARSAT, LIght Detection And Ranging - LIDAR).

Question 11

What are some attributes of new sensors and trends?

Answer 11

High resolution visible light satellites for sub-meter resolution.

Hyperspectral sensors that have hundreds of bands of data (instead of the 4-7 most commonly used in the past)

More timely coverage: ex. MODIS Terra and MODIS Aqua (36 bands 1-2 day revisit, low resolution – 250m or lower). Many of these are special purpose sensors for climate and pollution monitoring

Question 12

What is LIDAR imagery?

Answer 12

All the information seen here is a derived DEM including the trees and other objects above the ground surface.

• collected from planes
• an active sensor

Question 13

What are hyperspectral sensors?

Answer 13

These images do not appear any different from others because of display technology, but have dozens to hundreds of bands of wavelength data and are found useful for tough feature classification purposes (next time).

Question 14

What is MODIS?

Answer 14

moderate resolution imaging spectroradiometer

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Question 15

I need to get an image of a tropical rainforest area where it is never clear weather.  I will need to get my images from:
LANDSAT
Spot
Lidar
Radarsat
Modis

Answer 15

Radarsat

Question 16

I need to get a very accurate and high resolution elevation model.  I will need to get my image from:
LANDSAT
Spot
Lidar
Radarsat
Modis

Answer 16

Lidar

Question 17

How is remote sensing data in GIS?

Answer 17

1) Raw rectified images can be used as backdrops/basemaps for raster or vector GIS map data.
2) Classified data can be used as raster thematic layers for land cover, water bodies, turbidity, forest canopy, impervious surfaces, etc.
3) Band ratios like NDVI can produce raster maps of vegetation health. If you were farming a 10 square mile area in corn (not too far fetched these days), these images could tell you where to go and fertilize (lower NDVI than expected). Can also use these for crop yield predictions.
4) Like scanned maps, remote sensing imagery can be used as a source for digitizing. Map updates (new roads, etc.) can be made on-screen over images.