CH Geographic Information Systems 5

Question 1

Which coordinate system is most appropriate for measuring accurate distances and areas in a regional hydrographic survey covering a US coastal zone?

Accepted Answer

UTM (Universal Transverse Mercator) in NAD83

Answer

UTM zones in NAD83 provide a conformal projection with low distortion over limited east-west extents, making them standard for accurate distance and area measurements in US coastal surveys.

Question 2

In GIS-based hydrographic data quality assessment, what does 'completeness' refer to?

Accepted Answer

The degree to which all required features within the survey area are present and correctly attributed

Answer

Completeness in data quality assesses whether the dataset contains all features that should be present within the defined scope, including both commission (excess features) and omission (missing features) errors.

Question 3

A hydrographer uses a kriging interpolation to create a bathymetric surface. What does the semivariogram model describe?

Accepted Answer

The spatial autocorrelation structure — how depth similarity decreases with distance between sample points

Answer

The semivariogram models the spatial autocorrelation of the data, quantifying how quickly depth values become uncorrelated as distance increases, which drives the kriging interpolation weights.

Question 4

When integrating LiDAR topographic data with multibeam bathymetric data in a coastal GIS, what is the primary challenge at the land-sea interface?

Accepted Answer

Seamlessly merging surfaces that use different vertical datums and have different point densities in the intertidal zone

Answer

LiDAR uses orthometric or ellipsoidal heights while bathymetry references tidal datums, and both datasets have lower point density in the intertidal zone, making seamless integration challenging.

Question 5

In S-57 ENC data, the meta-object 'M_COVR' (Coverage) with CATCOV=1 indicates what about the sea area?

Accepted Answer

The area is covered by ENC data and is suitable for navigation use

Answer

CATCOV=1 on the M_COVR meta-object indicates that ENC coverage exists for that area, signifying that the data has been compiled and is available for electronic chart display systems.

(CH) Certified Hydrographer Practice Test

(CH) Certified Hydrographer Practice Test

CH Geographic Information Systems 5