Homework 3

For this HW you'll probably need a calculator to do some simple plane trigonometry.

Remember, if you get stuck, sketch the situation out on paper. The

class notes handed out last week on Platforms and Sensors should be consulted.  

Also, review the Canadian Center for Remote Sensing Tutorial chapter on Sensors

http://www.ccrs.nrcan.gc.ca/ccrs/learn/tutorials/fundam/fundam_e.html

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Q. 1: The space shuttle orbiting at 250 km underflies the Landsat

satellite orbiting at 750 km and, at the same instant, measures the

'brightness' of a particular ground cell using an identical sensor to

that on the satellite. a) What is the ratio of the ground resolution

cell sizes seen by the two instruments?, b) What is the ratio of the

absolute brightness values detected by the two sensors and why?

(assume uniform energy flux from the ground) [Hint: This question

tests understanding of energy flux and sensor height concepts] 

Q. 2: In remote sensing it is said that instruments cannot have arbitrarily

high spatial resolution and arbitrarily high spectral resolution at the

same time. Explain in a few sentences why you agree or disagree with

this statement. (Remember that spatial resolution corresponds to

ground resolution cell size, and spectral resolution corresponds to

detector bandwidth as illustrated in the figure at the end)

Q .3:

You have been hired by Acme Airborne Remote Sensing Services to provide

a technical evaluation of their new multispectral scanner system

designed to monitor the growth of commercial forests. Acme's new system

employs an across-track scanner that provides an instantaneous field of

view (IFOV) of 2.5 mrad (radians/1000) and a mirror capable of a 90 deg.

angular field of view. They plan to deploy the system on a Twin Otter

aircraft that cruises at 288 km/hour at an altitude of 8 km. From these

figures determine:

a) the size of the ground resolution cell (at nadir) in meters,

b) the swath width in kilometers, and

c) the number of ground resolution cells of the nadir cell size across the swath.

Acme wants to use a commercial grade of detectors that require a dwell

time/unit area of 1 micro-sec./sq. m (or more) in order to receive

enough EMR from the ground to function properly.

d) Given the above sensor and survey parameters, will the planned survey

be successful? To simplify the problem, assume that the mirror scans

completely across the swath in the time it takes the aircraft to move

forward by one row (line) of ground cells.

e) (bonus) If technical problems with Acme's survey do exist, what

pragmatic/economical changes to the experimental design would you make in order to

increase the chances of success?

Q .4:

The Advanced Very High Resolution Radiometer (AVHRR) is a cross-track

scanner that flies aboard a NOAA TIROS satellite at an altitude of 833

km. The orbital inclination is 98.9 deg., the AVHRR mirror scans

through +/-55.4 deg., and the detector system IFOV is 1.3

mrad. Determine:

a) The swath width in kilometers,

b) the ground resolution cell size at nadir, and

c) The ground resolution cell size at the swath edge.

d) Given the swath width, what problems might you anticipate in

interpreting refleccted visible and IR data for latitudes near the

roll-over

e) Give two common uses of AVHRR data (one for oceans, one for

continents) that are not strictly meteorological (Hint: take a look at

the measured wavebands).

Bonus Question: Define "Active" and "passive" remote sensing techniques,

giving examples of sensors that use each. List 1 or  2 advantages and

disadvantages of each appoach.