CH Remote Sensing & Satellite Imagery 3

Question 1

The Lyzenga log-ratio empirical method for satellite-derived bathymetry (SDB) is based on:

Accepted Answer

Logarithmic ratios of water-leaving radiance in two spectral bands calibrated with known depths

Answer

The Lyzenga method exploits the fact that different wavelengths attenuate at different rates with depth; by forming log-ratios of two bands and regressing against known control depths, a bathymetric model is derived.

Question 2

What minimum spatial resolution is generally required for satellite imagery used in detailed coastal harbor feature mapping?

Accepted Answer

Sub-meter to 1 meter (Very High Resolution class)

Answer

Resolving fine coastal features such as dock edges, navigation aids, and channel margins requires sub-meter to 1-meter resolution imagery from very high resolution commercial satellites.

Question 3

MODIS (Moderate Resolution Imaging Spectroradiometer) data is primarily used in hydrographic and oceanographic practice for:

Accepted Answer

Synoptic monitoring of ocean color, SST, and chlorophyll over large ocean areas

Answer

MODIS's 250 m–1 km resolution and 2,330 km swath make it ideal for large-scale, frequent monitoring of ocean color, sea surface temperature, sediment plumes, and chlorophyll-a concentrations.

Question 4

Ground truth depth data is essential in satellite-derived bathymetry (SDB) because it is required to:

Accepted Answer

Calibrate the empirical spectral-to-depth model and validate its accuracy

Answer

SDB models (empirical or physics-based) must be calibrated using independently measured depths from sonar or other sources, and the resulting model must be validated against withheld check points.

Question 5

Orthorectification of satellite imagery is performed to:

Accepted Answer

Remove geometric distortions caused by terrain relief displacement and sensor viewing geometry

Answer

Orthorectification uses a digital elevation model (or bathymetric model) and sensor parameters to correct for the apparent displacement of features caused by varying terrain elevation and off-nadir viewing angles.

(CH) Certified Hydrographer Practice Test

(CH) Certified Hydrographer Practice Test

CH Remote Sensing & Satellite Imagery 3