ICAR AICE-JRF/SRF Forest GIS, GNSS & LiDAR Analytics: practice questions

1 · GIS concepts: vector and raster data, projections, datums · hard

Why is the spherical Web Mercator projection used by many online base maps unsuitable for measuring forest area at high latitudes?

1. It shrinks areas strongly as latitude increases towards the poles
2. It inflates areas strongly as latitude increases
3. It cannot represent polygons, only raster tiles
4. It preserves area but distorts every angle

2 · Spatial analysis: overlay, buffer, terrain analysis · medium

A classified Landsat image has 12,000 forest cells of 30 m × 30 m. The forest area is:

1. 360 ha
2. 108 ha
3. 1,080 ha
4. 10,800 ha

3 · Spatial analysis: overlay, buffer, terrain analysis · medium

In the D8 flow-direction method, each DEM cell drains to:

1. All lower neighbours in proportion to their drop
2. The neighbour with the highest elevation
3. The steepest downslope of its eight neighbours
4. The nearest stream cell by straight-line distance

4 · Spatial analysis: overlay, buffer, terrain analysis · hard

Why do slopes computed from a 30 m satellite DEM tend to be lower than those from a 1 m LiDAR DTM on the same rugged terrain?

1. Satellite DEMs measure the ground beneath canopy
2. Coarse cells average out short steep features
3. LiDAR DTMs exaggerate elevation by the canopy height
4. Slope algorithms only work correctly on fine grids

5 · GNSS data collection and accuracy · medium

Which error source is especially severe for GNSS under a forest canopy?

1. Satellite clock drift caused by the canopy shading the antenna
2. Ionospheric delay produced by the leaves
3. Multipath from signals reflected by trunks and branches
4. Rounding of coordinates by the receiver display

6 · Airborne LiDAR: point clouds, canopy height models · medium

Why can airborne LiDAR map terrain beneath a closed forest when optical imagery cannot?

1. Laser light passes straight through leaves without reflection
2. LiDAR measures heat emitted by the soil surface
3. LiDAR uses microwaves that penetrate the canopy
4. Pulses passing through canopy gaps return from the ground

7 · Area-based and individual-tree LiDAR inventory · easy

In individual-tree detection, treetops are most commonly located as:

1. Local minima in the digital terrain model
2. Points with the highest return intensity
3. Local maxima in a smoothed canopy height model
4. Cells where last returns equal first returns

8 · Terrestrial and mobile laser scanning · medium

Why are multi-scan TLS designs used in forest plots instead of a single scan?

1. To increase the scanner's beam divergence
2. To avoid the need for any ground classification
3. To reduce occlusion of stems hidden behind others
4. To convert phase-shift data into time-of-flight data

9 · Open data and cloud platforms for forest monitoring · medium

GEDI, operating on the International Space Station, provides:

1. Spaceborne LiDAR samples of canopy height in 25 m footprints
2. Continuous wall-to-wall 1 m canopy height maps of the whole globe
3. C-band radar images that see through cloud
4. Daily 250 m optical images for fire detection

10 · Map production and cartographic standards · medium

Cartographic generalisation for a 1:250,000 overview map includes:

1. Adding every stand boundary from the 1:5,000 database
2. Selecting, simplifying and aggregating features
3. Increasing positional accuracy beyond that of the source
4. Reprojecting the data into geographic coordinates