Bathymetric & Benthic Mapping
The project seeks to test the feasibility of combining field observations from an along-track vessel-mounted sensor package with IKONOS or QuickBird commercial satellite imagery to monitor and map in detail the bathymetry and benthic habitats of Buccoo Reef and other reefs that fringe Tobago.
The objective of the pilot project (Phase 1) is to collect high resolution bathymetric and along-track substrate imaging data sets to be made available to the THA for use establishing a coral reef monitoring program, and in the revision of existing bathymetric charts.
The U.S. Geological Survey (USGS) has developed the Along Track Reef Imaging System (ATRIS) to acquire continuous digital still images of the sea floor during transects across shallow water reefs for use in the creation of benthic habitat maps. EXIF-format still images are acquired in autonomous mode via a Nikon D1x digital still camera mounted in a waterproof housing that is deployed on a pole attached to the survey vessel. Images are instantaneously transferred to a shipboard computer. Position and acquisition time obtained from a precision Wide Area Augmentation System (WAAS)-capable GPS receiver is sent to the camera, where it is incorporated into the header files of the EXIF format images. At the same time, navigation software in a separate computer is used to follow pre-planned transect lines and/or to collect a continuous log of the vessel’s position, typically at a one second rate. The GPS antenna is mounted on top of the camera pole, and accordingly the positions recorded are those of the camera as the images are acquired. A precision bathymetric sounder is mounted to the bottom of the camera pole continuously measures the height of the camera above the bottom. This camera-to-substrate range information is recorded by the navigation software for use in post-processing to determine the scale and bottom coverage area of each individual image.
The US Geological Survey Coastal and Marine Geology Program (USGS CMG) is collaborating with Buccoo Reef Trust Geographical Information System Unit (BRT GIS) to conduct a submerged topography survey at Buccoo Reef, Tobago.
The survey will be conducted using the USGS Along Track Reef Imaging System (ATRIS) deployed on a BRT survey vessel. The ATRIS system incorporates a Marimatech Model Esea-103 fathometer and narrow-beamed dual transducers that operate between 200-208 KHz frequencies to determine accurate sea bottom echo signals. The single-beam hydrographic sounder is capable of measuring submerged topography at a very fine-scale spatial resolution. Accurate geo-positioning is determined in post-processing software with dual-frequency carrier-phase differential GPS measurements from the boat made relative to a GPS base station at a nearby location. Motion compensators are used to minimize the effect of pitch and roll on the accuracy of the depth measurements.
The USGS Florida Integrated Science Center at St. Petersburg, FL has sent two field personnel to Tobago in January 15-25th, 2008, to mount the system on a BRT survey vessel and train BRT personnel, including an OJT youth intern and a visiting intern, on the use of the field equipment to acquire submerged topography data.
The BRT field crew will conduct the survey to map the entire reef platform at 10-m resolution boat-track spacing in the winter and spring of 2008. The acquired GPS and echo sounder data will be processed in the USGS FISC St. Petersburgh office and sent over to BRT for QA/QC. It is expected that a final DEM product of the Buccoo Reef will be published by the USGS at end of 2008.
This study was supported by the Buccoo Reef Trust, the Tobago House of Assembly (THA), the U.S. Geological Survey Center for Coastal and Watershed Studies, and the National Coral Reef Institute.
