ICAR AICE-JRF/SRF Remote Sensing, GIS & GNSS for Land & Water: practice questions

1 · The electromagnetic spectrum · medium

By the Stefan–Boltzmann law, if the absolute temperature of a blackbody doubles, its total emitted energy per unit area becomes

1. 8 times the original value
2. 4 times the original value
3. 16 times the original value
4. 2 times the original value

2 · The electromagnetic spectrum · medium

On a near-infrared image, a lake appears much darker than the surrounding cropland. The main reason is that

1. lakes are cooler than cropland and cooler surfaces reflect less near-infrared radiation
2. water absorbs nearly all near-infrared energy while crop canopies scatter it strongly
3. water scatters near-infrared energy sideways so that little reaches the sensor overhead
4. suspended sediment in the lake absorbs near-infrared energy that clear water would reflect

3 · Sensors, platforms and resolutions · medium

An image band has 30 m pixels. A classified paddy area contains 1200 pixels. What is the paddy area?

1. 1080 ha
2. 10.8 ha
3. 108 ha
4. 36 ha

4 · Sensors, platforms and resolutions · medium

An engineer must map paddy transplanting across a monsoon district where cloud cover persists for weeks. Which sensor type is most suitable?

1. A thermal infrared sensor, because clouds are transparent in the 8–14 µm window
2. A hyperspectral sensor, because narrow bands can separate cloud from standing water
3. A high-resolution optical sensor, because finer pixels see between the cloud gaps
4. Synthetic aperture radar, because active microwave imaging works through cloud

5 · Image classification · hard

Why is a single-date image often insufficient to separate two summer crops, and what is the usual remedy?

1. Crops never differ in the visible bands; the remedy is to classify only the near-infrared band
2. Their spectra can overlap on one date; multi-date data capture their different seasonal curves
3. Their spectra always differ on any date; the remedy is to use a finer radiometric resolution
4. Single-date images lack thermal bands; the remedy is to add a land surface temperature layer

6 · GIS data models · medium

On the Mercator projection, the scale factor at latitude φ is sec φ. How much is area exaggerated at 60° latitude compared with the equator?

1. 1.4 times
2. 2 times
3. 8 times
4. 4 times

7 · GNSS · hard

A surveyor notices that PDOP rises sharply when most visible satellites are clustered low in the eastern sky. Why?

1. Clustered satellites broadcast on the same frequency and jam each other's signals
2. Clustered satellites give poor geometry, so range errors map into large position errors
3. Low satellites are closer to the receiver, which shortens the ranges below the error level
4. Low satellites always have more accurate clocks, which disturbs the least-squares solution

8 · Applications to watershed, irrigation and erosion mapping · hard

A GIS-based groundwater prospect map rates a village as a 'very good' zone. What does this mean for siting a borewell?

1. It shows the measured depth to the water table, so the well depth can be set from the map
2. It guarantees a yield above the state norm, so drilling can proceed without further survey
3. It indicates higher likelihood; a geophysical survey or test drilling must confirm the aquifer
4. It means the aquifer is recharged by canals, so yields will not decline in dry years

9 · GIS data models · medium

What is a triangulated irregular network (TIN)?

1. A network of stream lines coded by Strahler order for hydrological analysis
2. A raster of equal square cells, each storing a single height value for its area
3. A surface model of non-overlapping triangles joining irregularly spaced height points
4. A set of contour lines stored as closed polygons with a height attribute each

10 · Spatial analysis · medium

Reclassifying a slope raster into classes 1 (0–3%), 2 (3–8%) and 3 (above 8%) is an example of

1. a local operation that changes each cell's value independently of its neighbours
2. a global operation that needs every cell to compute the value of each cell
3. a focal operation that uses a moving 3 × 3 window around each cell
4. a zonal operation that summarises values inside separate polygon zones