Mixed Deck — All CH Topics Flashcards

A hydrographer notices that a restored reach has a sinuosity ratio of 1.05. What does this indicate?

Answer: The channel is nearly straight, suggesting possible under-restoration

A sinuosity ratio near 1.0 indicates an almost straight channel; reference reaches for the same valley slope typically have higher sinuosity.

What is multi-factor authentication in CH security?

Answer: Requiring two or more verification factors for access

MFA requires multiple verification factors (knowledge, possession, biometrics), significantly reducing unauthorized access.

What is change management in CH technology?

Answer: A structured process for evaluating and implementing changes safely

IT change management ensures changes are evaluated, approved, tested, and implemented in a controlled manner.

A geodetic baseline measured along the Earth's surface is 10 000 m. What type of line connects the two endpoints with the shortest path on the ellipsoid?

Answer: Geodesic

A geodesic (or geodetic line) is the shortest path between two points on the surface of an ellipsoid, analogous to a great circle on a sphere.

What is the purpose of the S-57 Object Catalog in hydrographic GIS?

Answer: It defines all permissible object classes, attributes, and their relationships for ENC data

The S-57 Object Catalog (IHO Publication S-57 Appendix A) defines the complete dictionary of feature classes and attributes allowed in Electronic Navigational Charts.

Satellite radar altimetry contributes to hydrography and geodesy primarily by providing:

Answer: Sea surface height measurements used to model mean sea level and the marine geoid

Radar altimeters precisely measure sea surface height relative to a reference ellipsoid; these measurements underpin mean sea level determination, geoid modeling, and ocean circulation studies.

A stream's assimilative capacity refers to its ability to:

Answer: Receive and break down pollutants without violating water quality standards

Assimilative capacity is the amount of waste a water body can absorb through natural processes without exceeding water quality criteria.

Which orbit type do most hydrographic Earth observation satellites use to achieve consistent global coverage?

Answer: Sun-synchronous Low Earth Orbit (LEO)

Sun-synchronous LEO orbits ensure the satellite crosses each latitude at the same local solar time, providing consistent illumination conditions and global coverage with frequent revisits.

When computing the grid azimuth from a geodetic azimuth in UTM, which correction must be applied?

Answer: Meridian convergence (γ)

Meridian convergence γ is the angle between grid north and geodetic (true) north at any point off the central meridian; grid azimuth = geodetic azimuth − γ.

What is multi-factor authentication in CH security?

Answer: Requiring two or more verification factors for access

MFA requires multiple verification factors (knowledge, possession, biometrics), significantly reducing unauthorized access.

Conductivity measurements in streams primarily reflect the concentration of:

Answer: Dissolved ions and salts

Electrical conductivity increases with dissolved ion concentration; high conductivity often signals elevated salinity or mineral content.

According to USGS Techniques and Methods 3-A22, the recommended minimum number of transects for a standard ADCP discharge measurement is:

Answer: 4 transects

USGS guidance recommends a minimum of four transects (two in each direction) to obtain a reliable mean discharge estimate and assess measurement repeatability.

What is the angular difference called between astronomic north (defined by Earth's rotation axis) and geodetic north (defined by the ellipsoid normal)?

Answer: Deflection of the vertical

The deflection of the vertical is the angle between the gravity vector (plumb line) and the ellipsoidal normal, separating astronomic and geodetic latitudes/longitudes.

What is the primary reason hydrographers must apply a sea-level correction factor when working in high-elevation inland waterways?

Answer: Grid distances on the projection are shorter than ground distances

At elevation, the Earth's surface is farther from the projection plane, so grid distances underestimate ground distances; the sea-level (elevation) factor corrects for this.

Which method best quantifies the total dissolved load exported from a watershed for sustainable nutrient management?

Answer: Continuous streamflow gauging combined with periodic water quality sampling (load = Q × C)

Nutrient load is calculated as the product of discharge (Q) and concentration (C); continuous flow records combined with sample data yield accurate export estimates.

Which spatial reference system is most commonly used for global marine navigation data in hydrographic GIS applications?

Answer: WGS84

WGS84 is the standard geodetic datum used globally for GPS and marine navigation, making it the default for hydrographic GIS datasets.

Which software function helps identify outliers in bathymetric datasets?

Answer: Data cleaning

Data cleaning, often performed using specialized hydrographic software, is the process of identifying and removing erroneous or anomalous data points (outliers) from bathymetric datasets. These outliers can result from noise, multipath reflections, or sensor malfunctions. Effective data cleaning is essential to ensure the accuracy and reliability of the final seafloor model, preventing misinterpretations and ensuring safe navigation.

What is the hydrographic significance of 'blue carbon' ecosystems such as mangroves and seagrass beds?

Answer: They sequester carbon and stabilize sediment, making their mapping critical for climate and coastal management

Blue carbon ecosystems store large amounts of organic carbon and reduce erosion; hydrographic mapping identifies their distribution and supports their protection.

What is 'acoustic backscatter' data collected during multibeam surveys primarily used for?

Answer: Characterizing seafloor sediment type and habitat classification

Acoustic backscatter intensity reflects how much sonar energy returns from the seafloor, which varies with sediment type, roughness, and hardness, enabling bottom classification.

In raster GIS, what does 'resampling' refer to when changing the cell size of a bathymetric grid?

Answer: Recalculating cell values when converting between grid resolutions using methods like nearest neighbor or bilinear interpolation

Resampling recalculates cell values when a raster is reprojected or rescaled, using algorithms like nearest neighbor, bilinear, or cubic convolution to estimate new cell values.