GEOG 551: Principles of Remote Sensing
Exercise #5
Analysis and Interpretation of Radar Imagery
Due Date: October 31, 2006
Please note : It is essential to employ correct units (cm, km, sec) in performing these calculations. Please show all of your work.
The unique feature of imaging radar is its ability to collect data over virtually any region at any time, regardless of weather or sunlight conditions. Some radar waves can penetrate clouds, and under certain conditions, can also see through vegetation, ice and extremely dry sand. In many cases, radar is the only way scientists can explore inaccessible regions of Earth's surface.
Radar is a lowercase acronym for "radio detection and ranging". A synthetic aperture radar transmits pulses of microwave energy toward Earth and measures the strength and time delay of the energy that is scattered back to the antenna. In the case of SIR-C/X-SAR, the motion of the shuttle is used to "synthesize" an antenna (the aperture) that is much longer in length than the actual antenna hardware. A longer antenna produces images of finer resolution.
Conditions on the Earth's surface influence how much radar energy is reflected back to the antenna. An area with a variety of surface types, such as hills, trees and large rocks, will generally reflect more energy back to the radar than a less complex area such as a desert. The resulting radar image of the varied terrain will be brighter overall than the image of the simpler area.
1. A SLAR (Side-Looking Airborne Radar) system with a pulse length, τ, of 0.1 x 10-6 seconds is used to obtain images of targets at a depression angle, γ, of 30 degrees.
a. According to the equation discussed in the lecture, the range resolution, Rr, is how many meters?
b. How many meters would Rr be if the pulse length were 0.05 x 10-6 seconds?
c. How many meters would Rr be if the depression angle were 15 degrees?
2. You have been commissioned by the U.S. Forest Service to conduct a SLAR mission to resolve and count rows of planted pine that are spaced at intervals of 20 meters. The pilot for this mission proposes a flight plan that would image trees at a depression angle of 20 degrees.
a. For a SLAR system with a pulse length of 0.1 x 10-6 seconds, will the trees be resolved? Explain your answer.
b. Describe two equipment modifications that could be made on the SLAR sensor system to improve range resolution Rr?
3. An X-band (wavelength λ = 3cm ) real aperture SLAR antenna has a length, D , of 400 cm. For a slant range distance, S , of 40 km , use the equations discussed in lecture to calculate resolution in azimuth direction.
a. How many meters is the azimuth resolution Ra ?
The above configuration will be used to acquire images of pine trees that are spaced at distances of 100 m in the azimuth direction.
b. What is the maximum slant range, S, at which the pilot can fly the mission and still be able to resolve the trees?
a. Complete the following table:
| Roughness Category |
Ka Band ( = 0.86 cm) |
X Band ( = 3.0 cm) |
L Band ( = 25.0 cm) |
|---|---|---|---|
| Smooth | h < _______cm | h < _______cm | h < _______cm |
| Intermediate | h = _______cm | h = _______cm | h = _______cm |
| Rough | h > _______cm | h > _______cm | h > _______cm |
b. How does radar spectral response relate to the computed surface roughness criteria?
5. A geologist needs to distinguish talus ( h = 12.0 cm ) from gravel deposits ( h = 1.5 cm ).
a. According to the above table, the geologist should employ a radar image acquired at a wavelength of how many centimeters?
b. What kind of return do you expect from tallus? How would it appear on the image?
c. What kind of return do you expect from tallus? How would it appear on the image?
6. A radar image is acquired using the following parameters:
Real Aperture Ka band (wavelength λ = 0.86 cm )
Pulse Length τ = 0.1 microsecond
Depression Angles (γ)
50 degrees in the near range
42 degrees in the mid range
35 degrees in the far range
a. Compute the range resolution Rr in the following:
Near range ____________
Mid range ____________
Far range _____________
b. Compute the smooth, intermediate, and rough criterion for this imagery in the mid range.Smooth _____________ cm
Intermediate _____________ cm
Rough ______________ cm
River Water
Boats
Urban Areas
Road Networks
Agricultural Areas
7. Geophysical evidence suggests that lineaments in an exploration area may trend 60 degrees from North.a. In order to enhance these lineaments, what are the two optimum radar look directions?
The terrain of this study area has little topographic relief and the lineaments are marked by low scarps, ridges, and minor depressions.
b. Will these lineaments be best expressed in the near or far range portion of the image strip? Explain your answer.
|
|
8. Assume that the two images above are oriented with north at the top. These images are X-band HH polarization.
a. The look direction for image A is:
b. The look direction for image B is:
 |
|
9. The above image is a RADARSAT scene (C-band, HH polarization) of the Catskill Mountains in southeastern NY along the Hudson River. The image was acquired in Fine Beam Mode which offers a 37.99 degree incident angle and 10 x 10 m resolution.
a. Based on your readings, what is the look direction?
b. What elevation-induced effect is prevalent on the montainous area of this iamge and why does it occur?
Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. Radars illuminate the Earth with microwaves, allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: the L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency data is used by the international scientific community to better understand the global environment and how it is changing. The SIR-C/X-SAR data, complemented by aircraft and ground studies, gives scientists clearer insights into those environmental changes which are caused by nature and those changes which are induced by human activity.
|
|
| Los Angeles, CA | San Francisco, CA |
|---|
The radar image on the left is of Los Angeles, California, taken on October 2, 1994. This single- frequency SIR-C image was obtained by the L-band (24 cm) radar channel, horizontally transmitted and received. Suburban areas, with the low-density housing and tree-lined streets that are typical of Los Angeles, appear as lighter grey. Scientists hope to use radar image data from SIR-C/X-SAR to map fire scars in areas prone to brush fires, such as Los Angeles. In this image, the Altadena fire area is visible in the top center of the image as a patch of mountainous terrain which is slightly darker than the nearby mountains.
The radar image on the right is of San Francisco, California, taken on October 3, 1994. Downtown San Francisco is visible in the center of the image with the city of Oakland east (to the right) across San Francisco Bay. Also visible in the image is the Golden Gate Bridge (left center) and the Bay Bridge connecting San Francisco and Oakland. North of the Bay Bridge is Treasure Island. Alcatraz Island appears as a small dot northwest of Treasure Island. This single-frequency SIR-C image was obtained by the L-band (24 cm) radar channel, horizontally transmitted and received. Viewing of additional SIR-C/X-SAR radar images may be viewed by going to the Jet Propulsion Lab's SIR-C/X-SAR Space Radar Images of the Earth website: http://www.jpl.nasa.gov/radar/sircxsar/.
10. For the following questions, assume a typical depression angle of 45 degrees:
RADARSAT and JERS IMAGE COMPARISON of TIVOLI SOUTH BAY, NYa. Why do flat surfaces, such as the Pacific Ocean, freeways, and airport runways appear very dark in the image?b. Why are there brighter patches of radar illumination on the mountain slopes?
c. Suburban areas, with the low-density housing and tree-lined streets that are typical of Los Angeles or San Francisco, appear as lighter grey. Why do you suppose areas with high-rise buildings, such as in the downtown areas, appear in very bright white?
 |
|
 |
| RADARSAT (C-band, HH polarization) August 10, 1998 |
JERS-1 (L-band, HH polarization) July 3, 1993 |
Photograph acquired at location (a) of water chestnut floating on the majority of the surface of Tivoli South Bay. |
|---|
The RADARSAT SAR is a C-band system (5.6 cm wavelength) with HH polarization. RADARSAT's Fine Beam Mode offers a 37.99 degree incident angle and 10 x 10 m resolution. The JERS-1 SAR is an L-band system (23.5 cm wavelength) with HH polarization, 38.5 degree incident angle, and 18 x 18 m resolution.
11. Explain why the radar return is different between C-band and L-band for water chestnut leaves floating on the surface of Tivoli South Bay?
12. For the following applications, choose the radar microwave band (K, X, C, S, L, P) that you would use and explain your reasoning:
a. Estimating soil moisture-b. Discriminating of crop type-
c. Monitoring storm activity-
d. Determining the extend of flooded surfaces in a heavily forested canopy-
e. Obtaining accurate measurements of swelling or buckling in seismically active areas-
f. Detecting buried river channels in hyper-arid environments-
g. Mapping of oil slicks-
