Educational Module #2: Benthic Educational Module #2: Benthic Terrain ClassificationTerrain Classification

Emily M. Larkin and Dawn WrightEmily M. Larkin and Dawn WrightDept. of Geosciences, Oregon State Dept. of Geosciences, Oregon State

UniversityUniversitySeptember, 2004September, 2004

(Larkin 2001)

ObjectivesObjectives

• On completion of the project, you should be able to:– Do a slope analysis.– Use Raster Calculator to do simple

analyses.– Use Grid to process a short command

sequence that is given to you.– Define: Slope, Bathymetric Position

Index, benthic, standard deviation and benthic zones.

Benthic Terrain Benthic Terrain ClassificationClassification•Benthic = of or pertaining to the

seafloor. (e.g. A benthic animal lives on the seafloor.)

•Bathymetry can be classified into different zones based on what type of terrain it is.

SlopeSlope•Slope is steepness

of the landscape

•Percent Slope = Rise / Run * 100%

•Degree Slope = the measure of the slope angle

Rise

Run

Slope Angle(Degree)

Bathymetric Position Index Bathymetric Position Index (BPI)(BPI)• BPI finds out

where a pixel is in relationship to its neighbors.

• Raster calculator compares the position of a pixel to those around it.

(after Weiss 2001)

Bathymetric Position IndexBathymetric Position Index

•BPI is calculated at a user-defined scale. – The resolution of the grid * the outer

radius in the BPI equation– Fine-scale BPI—looks at small features

(e.g small crests on a large slope)– Broad-scale BPI—looks at large features

(e.g. the large slope)

Benthic ZonesBenthic Zones

• Divide bathymetry into 4 zones: flats, slopes, crests and depressions

• Benthic zones have been linked to biodiversity (Karlson et al. 2004)

• Based on: – Slope—greater or less than 5%– Broad-scale BPI—less than or greater than 1

standard deviation from the mean

• WARNING—When you get to this part of the lesson, you must type everything correctly! Go slow and double-check.

Module #2Module #2

•Bathymetry from Pago Pago Harbor

•Slope Analysis

•BPI

•Benthic Zone Classification

Error Correction--Error Correction--

•Note: On Page 12, Step 1 should read:– Add ppg5m84_neg. In the Spatial

Analyst…– Step 1a—Make sure the

ppg5m84_neg grid is showing…