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Depth is calculated from sound wave velocity and time travelled through the water column. Bathymetry surveys that record sound velocities through the water column provide more accurate estimates of seabed depth because variations in water density are accounted for. The time it takes for a sound wave to propagate through the water column, reflect off the seabed and reach a sensor is known as two-way travel time, which is the typical format for echo sounder data.
Measurement type: | Depth |
File format: | GeoTIFF |
File: |
|
Data type: | 32bit floating point |
Data/Pixel units | metres |
Band number: | 1 |
Description: | Distance from the seabed to sea surface in metres. Depth is a negative value which displays elevation as a positive value. |
No data value: | NaN |
Valid data range: | [0 to –12,000] |
Tiled with X and Y block sizes: | [512, 512] |
Compression: | Deflate, Level-6 predictor-3 |
Pyramids: | Yes . Levels will be [8, 16, 32]. Compress the pyramids using deflate. Bi-linear resampling |
Output Coordinate Reference System (CRS): | EPSG 4326 (geographic decimal degrees); except where source is UTM using WGS84 |
Horizontal Datum: | WGS84 |
H_Output Units: | Variable (Geographic - decimal degrees, UTM – metres) |
Vertical Datum: | EGM2008 height (EPSG:3855) |
V_Output Units: | metres |
Output name: | filename || _OV.TIFF |
Table 4. Format specifications for a single band MBES depth GeoTIFF.
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Density is the measure of soundings per area. The higher the density, the more robust and higher resolution the bathymetry data. In this case, density is determined by the number of soundings per node, where a node is a grouping of sounding points with similar elevation. High density bathymetry data typically occurs in the middle of the beam swath and density lowers closer to the edges of a swath.
Measurement type: | Density |
File format: | GeoTIFF |
File: |
|
Data type: | 16bit Unsigned Integer (UInt16) |
Data/Pixel Units | Count (Frequency counts of points per pixel) |
Band number: | 1 |
Description: | Number of soundings per cell/node. A node forms a cell in a bathymetry grid with a value displaying density, which is derived from the number of soundings within that node. Sounding density can inform optimal bathymetry data resolution. |
No data value: | 0 |
Valid data range: | [0, 65535] |
Tiled with X and Y block sizes: | [512, 512] |
Compression: | Deflate, Level-6 predictor-2 |
Pyramids: | None |
Output Coordinate Reference System (CRS): | Output Coordinate Reference System (CRS): EPSG 4326 (geographic decimal degrees); except where source is UTM with WGS84 as the datum |
Horizontal Datum: | WGS84 |
H_Output Units: | Variable (Geographic - decimal degrees, UTM – metres) |
Vertical Datum: | EGM2008 height (EPSG:3855) |
V_Output Units: | metres |
Output name: | filename || .TIFF |
Table 5. Format specifications for a single band MBES density GeoTIFF.
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Uncertainty is the measure of sounding confidence and is calculated from the distance between a sounding point and a node (a node is a grouping of points with similar elevation). The greater the value, the more uncertain is the point’s depth value. Influencing factors include depth, point density, proximity to swath edge and acquisition system horizontal and vertical uncertainties.
Measurement type: | Uncertainty |
File format: | GeoTIFF (32bit floating point) |
File: |
|
Data type: | Float32 |
Data/Pixel Units | Uncertainty (preferred) and/or Standard Deviation (only if CUBE is used) decimals |
Band number: | 1 |
Description: | A measure of a soundings confidence that is a proxy for horizontal and vertical accuracy. A higher density of soundings contributes to lowering uncertainty. Calculated from the distance a sounding is from a cell/node. When filtering, an uncertainty of 2 contains 95% of points closest to a cell/node. |
No data value: | NaN |
Valid data range: | – [0, 1], inf |
Tiled with X and Y block sizes: | [512, 512] |
Compression: | Deflate, Level-6 predictor-3 |
Pyramids: | None |
Output Coordinate Reference System (CRS): | EPSG 4326 (geographic decimal degrees); except where source is UTM with WGS84 as the datum |
Horizontal Datum: | WGS84 |
H_Output Units: | Variable (Geographic - decimal degrees, UTM – metres) |
Vertical Datum: | EGM2008 height (EPSG:3855) |
V_Output Units: | metres |
Output name: | filename || .TIFF |
Table 6. Format specifications for a single band MBES uncertainty GeoTIFF.
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Hillshading is a technique for visualizing terrain determined by a light source and the slope and aspect of the elevation surface. It is a qualitative method for visualizing topography and does not give absolute elevation values. This is a derivative product of the L3 MBES Bathymetry grid (GeoTIFF).
Measurement type: | Hillshade |
File format: | GeoTIFF |
File: |
|
Data type: | UINT8 |
Data/Pixel Units | unitless |
Band number: | 1 |
Description: | Hillshade |
No data value: | 0 |
Valid data range: | 1-255 |
Tiled with X and Y block sizes: | [512, 512] |
Compression: | Deflate, Level-6 predictor-3 |
Pyramids: | Yes Levels will be [8, 16, 32]. Compress the pyramids using deflate. Bi-linear resampling |
Output Coordinate Reference System (CRS): | Output Coordinate Reference System (CRS): EPSG 4326 (geographic decimal degrees); except where source is UTM with WGS84 as the datum |
Horizontal Datum: | WGS84 |
H_Output Units: | Variable (Geographic - decimal degrees, UTM – metres) |
Vertical Datum: | EGM2008 height (EPSG:3855) |
V_Output Units: | metres |
Output name: | filename || .TIFF |
Table 7. Format specifications for a single band Hillshade GeoTIFF.
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