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Ground Validation

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Ground Validation / Training Fieldwork

A total of 566 field stations were occupied for ground validation and training data throughout the Hawaiian Islands where imagery was collected (e.g. Figure 1). Ground validation was also conducted in the Northwestern Hawaiian Islands in 2002.

Map of O‘ahu indicating placement of stratified random sampling stations in the Kāne‘ohe Bay accuracy assessment test area (red points), specifically located ground control points used in image orthorectification (yellow points), and ground validation stations used to train photointerpreter during second generation map production (blue points). Map in UTM zone 4 North using NAD 83 datum with distance in meters.

These ground validation stations functioned as training data or ground truthing for the photointerpreter. Their locations were specifically chosen by the photointerpreter based on features seen but not identified in the imagery. Data collected at each station included precise GPS coordinates, time, date, water depth, relative topographic relief, and automatically generated GPS statistics associated with the positional data. Underwater photographs were also collected for a subset of field stations.

The main reason for occupying each ground validation station was to determine what detailed habitat class to assign to the feature or polygon seen in the imagery. Confusing or difficult to interpret features were identified and characterized in the field. These identifications had to conform to the classes of the Hawai‘i benthic habitat classification scheme for subsequent mapping and accuracy assessment to be valid. The same observer made all the characterization calls by either breath-hold diving, viewing the substrate through a glass-bottom look box, or observing from the surface in shallow water conditions.

The ground validation GPS data were differentially corrected to the nearest available continuously operating reference station (CORS), and all attributes associated with the data were checked for errors or blunders. The underwater digital photographs were also downloaded and named according to the unique sampling station ID number.


Last Update: 04/21/2008

By: Lea Hollingsworth

Hawai‘i Coral Reef Assessment & Monitoring Program

Hawai‘i Institute of Marine Biology

P.O. Box 1346

Kāne‘ohe, HI 96744

808-236-7440 phone

808-236-7443 fax