CFS Technology & Digital Tools 3 — Questions and Answers
Question 1: A floodplain surveyor wants to assess changes in channel morphology over a 10-year period. Which remote sensing approach is most appropriate?
- Multi-temporal satellite imagery analysis (Correct answer)
- Single-flight LiDAR survey
- Ground-penetrating radar
- Acoustic Doppler current profiler
Correct answer: Multi-temporal satellite imagery analysis
Comparing satellite or aerial imagery from different dates (multi-temporal analysis) reveals planform channel changes, bank migration, and sediment deposition over time.
Question 2: In the context of Elevation Certificates, eBFE stands for:
- Estimated Base Flood Elevation (Correct answer)
- Electronic BFE lookup tool
- Emergency Backup Flood Elevation
- Effective BFE reference datum
Correct answer: Estimated Base Flood Elevation
eBFE refers to the Estimated Base Flood Elevation, used when a site-specific BFE has not been formally established through a FIRM study.
Question 3: Which coordinate reference system is mandatory for all FEMA National Flood Hazard Layer (NFHL) data submissions?
- NAD 83 geographic or state plane coordinates (Correct answer)
- WGS 84 UTM only
- NAD 27 state plane
- Local assumed datums are acceptable
Correct answer: NAD 83 geographic or state plane coordinates
FEMA requires NFHL data to be referenced to NAD 83, using geographic or state plane coordinates depending on the delivery specification.
Question 4: Bathymetric LiDAR differs from topographic LiDAR in that it uses:
- Green (532 nm) laser pulses that penetrate shallow water (Correct answer)
- Infrared pulses that reflect off the water surface
- Radar waves instead of laser pulses
- Passive thermal imaging
Correct answer: Green (532 nm) laser pulses that penetrate shallow water
Bathymetric LiDAR uses a green-wavelength laser (~532 nm) that can penetrate clear, shallow water to map underwater topography.
Question 5: When a surveyor submits a Letter of Map Amendment (LOMA) digitally through FEMA's eLOMA tool, the key advantage over paper submissions is:
- Faster processing with near-instant preliminary determinations for qualifying properties (Correct answer)
- Higher accuracy elevation data acceptance
- Automatic field verification by FEMA
- Elimination of the need for an Elevation Certificate
Correct answer: Faster processing with near-instant preliminary determinations for qualifying properties
FEMA's eLOMA tool provides near-instant preliminary LOMA determinations for simple cases, dramatically reducing processing time compared to paper submissions.
Question 6: In a GIS flood model, Manning's n roughness values are typically applied using which spatial data layer?
- Land use / land cover raster or polygon layer (Correct answer)
- Digital elevation model raster
- Census boundary shapefile
- FIRM Q3 flood zone layer
Correct answer: Land use / land cover raster or polygon layer
Manning's n values are assigned to hydraulic model cells based on land use/land cover classifications derived from raster or vector polygon data.
Question 7: A UAV (drone) survey for floodplain mapping uses Structure-from-Motion (SfM) photogrammetry to produce which primary deliverable?
- Dense point cloud and orthomosaic imagery (Correct answer)
- Real-time flood inundation extent
- Subsurface soil stratigraphy
- Stream discharge hydrograph
Correct answer: Dense point cloud and orthomosaic imagery
SfM processing of overlapping UAV imagery generates a dense 3D point cloud and a georeferenced orthomosaic, which can be used to create a high-resolution DEM.
CFS Technology & Digital Tools 3
A floodplain surveyor wants to assess changes in channel morphology over a 10-year period.
Which remote sensing approach is most appropriate?