SHOALS

These data are originated from US Army Engineer Joint Airborne LIDAR Bathymetry Technical Center of Expertise (JALBCTX), which were collected by the SHOALS (Scanning Hydrographic Operational Airborne LIDAR Survey) system. The SHOALS system consists of an airborne laser transmitter/receiver capable of measuring 400 soundings per second. The system operates from a deHavilland DHC-6 Twin Otter flying at altitudes between 200 and 400 meters with a ground speed of about 100 knots. The SHOALS system also includes a ground-based data processing system for calculating accurate horizontal position and water depth. LIDAR is an acronym for Light Detection And Ranging. The system operates by emitting a pulse of light that travels from an airborne platform to the water surface where a small portion of the laser energy is backscattered to the airborne receiver. The remaining energy at the water's surface propagates through the water column and reflects off the sea bottom and back to the airborne detector. The time difference between the surface return and the bottom return corresponds to water depth. The maximum depth the system is able to sense is related to the complex interaction of radiance of bottom material, incident sun angle and intensity, and the type and quantity of organics or sediments in the water column. As a rule-of-thumb, the SHOALS system should be capable of sensing bottom to depths equal to two or three times the Secchi depth. SHOALS has demonstrated capabilities that meet US Army Corps of Engineers Hydrographic Survey accuracy requirements for Class 1 surveys and the International Hydrographic Organization nautical charting standards for Order 1.

Kauai and Maui coastline survey was collected from February to April 1999. Oahu coastline survey was collected from March to April 1999 Molokai and Lanai coastline survey was collected in November 2000. The projection is geographic, the units are decimal degrees, and Datum is WGS84. The depth are in meters from Mean Lower Low Water. The horizontal positional accuracy is +/- 3 meters (1 sigma), and the vertical positional accuracy is +/- 15 cm (1 sigma).