Remote Sensing
Remote sensing, including aerial photography, digital imagery, and LiDAR expand the coverage of resource monitoring projects in the Colorado River Ecosystem (CRE). GCMRC Survey Department supports remote sensing operations by both providing positioning of imagery data, and by verifying positions derived from the imagery data. Two methods of ortho-rectifying imagery data acquired by GCMRC are airborne GPS positioning and ground control point positioning. Airborne positioning references GPS data collected on board the aircraft to GPS data collected from one or more base stations. Members of the GCMRC survey department occupy known, fixed, rim control points with GPS receivers during the overflight. These occupations are used as base stations for kinematic post processing with the airborne GPS data. Ideally, the airborne GPS data is referenced to multiple base stations for the most accurate positioning.
Ground control point positioning assigns coordinate values to ground features visible on the imagery. Generally, this method of image positioning entails either laying ground panels or selecting precise features visible on the imagery and assigning them coordinate values. The GCMRC Survey Department sets the panels prior to an over flight, surveys the position of the panels, and subsequently removes the panels, or selects features from overflight imagery and subsequently surveys the position of the feature. The surveyed positions are referenced to a point in the control network to ensure high accuracy.
Aerial imagery and LiDAR provide alternative methods of collecting monitoring data over large areas without the need of a river trip. Remotely sensed imagery supports the following projects: Sediment monitoring, Sediment modeling, Campsite beach monitoring, Channel morphology, Terrestrial vegetation monitoring, and mitigation of damage to cultural resources.