CFS Technology & Digital Tools 2 — Questions and Answers
Question 1: Which file format is the standard for exchanging LiDAR point cloud data used in floodplain elevation mapping?
- LAS/LAZ (Correct answer)
- GeoTIFF
- Shapefile
- KML
Correct answer: LAS/LAZ
LAS (and its compressed variant LAZ) is the industry-standard binary format for storing airborne LiDAR point cloud data.
Question 2: In GIS-based floodplain analysis, a Digital Elevation Model (DEM) derived from LiDAR typically has a horizontal resolution of:
- 1–3 meters (Correct answer)
- 30 meters
- 100 meters
- 500 meters
Correct answer: 1–3 meters
Modern LiDAR-derived DEMs for floodplain mapping commonly achieve 1–3 meter horizontal resolution, far superior to older 30-meter SRTM data.
Question 3: What does the acronym GNSS stand for in the context of field surveying for floodplain studies?
- Global Navigation Satellite System (Correct answer)
- Geographic Network Surveying System
- Ground Node Spatial Sensor
- Geospatial Navigation and Sounding System
Correct answer: Global Navigation Satellite System
GNSS encompasses all satellite constellations (GPS, GLONASS, Galileo, BeiDou) used for positioning, making it the broad term surveyors use.
Question 4: A surveyor uses Real-Time Kinematic (RTK) GNSS for establishing benchmark elevations in a floodplain survey. The primary advantage of RTK over static post-processing is:
- Centimeter-level accuracy delivered in real time (Correct answer)
- Lower equipment cost
- No need for a base station
- Compatibility with NAVD 29 only
Correct answer: Centimeter-level accuracy delivered in real time
RTK GNSS uses a base station broadcasting corrections to achieve centimeter-level positional accuracy instantly in the field.
Question 5: When using FEMA's Map Service Center (MSC) online, a floodplain surveyor can primarily retrieve:
- Official FIRM panels and FIS reports (Correct answer)
- Real-time stream gauge data
- LiDAR point cloud downloads
- GNSS base station corrections
Correct answer: Official FIRM panels and FIS reports
FEMA's MSC is the official portal for accessing current Flood Insurance Rate Map (FIRM) panels and Flood Insurance Study (FIS) reports.
Question 6: In HEC-RAS 2D hydraulic modeling, what grid cell size consideration is most critical when modeling an urban floodplain with narrow conveyance channels?
- Cell size must be small enough to resolve channel geometry (Correct answer)
- Cell size should match the DEM resolution exactly
- Larger cells reduce computational error in urban areas
- Cell size only matters for 1D models
Correct answer: Cell size must be small enough to resolve channel geometry
In 2D HEC-RAS, the computational mesh must be fine enough to capture channel cross-section geometry; overly coarse cells miss critical conveyance pathways.
Question 7: Which FEMA tool allows communities to view and comment on preliminary FIRM data before they become effective?
- FEMA Mapping Information Platform (MIP) (Correct answer)
- National Flood Hazard Layer (NFHL) viewer
- HEC-HMS
- National Water Model dashboard
Correct answer: FEMA Mapping Information Platform (MIP)
The FEMA Mapping Information Platform (MIP) is the project management and data submission portal where communities review preliminary flood maps.
CFS Technology & Digital Tools 2
Which file format is the standard for exchanging LiDAR point cloud data used in floodplain elevation mapping?