GPS surveys within Falls Creek: Implementation and processing for aerial photography

This paper details GPS surveys undertaken in Falls Creek Ski Resort for a research project. Static, rapid-static and RTK GPS surveys were undertaken to establish a framework of accurate positional points with in the study area. Campaigns involved control surveys, coordination of photo control and elevation profiles, utilising the different GPS positioning techniques listed. The logistical problems of coordinating survey marks in areas of sparse survey control, deploying photo control targets over snow for image acquisition are discussed. The imagery acquired, in both winter (snow cover) and spring (no-snow cover), was later used to create surface models. The required positional accuracies resulting from the GPS surveys, for the photogrammetric validation purposes, were <20 mm for both Easting and Northing (MGA94, Zone 55), and <50 mm for elevation (AHD). The required post-processing and the results of rigorous network adjustment are also detailed. GPS static data was network adjusted from simultaneous state-wide GPSnet data using MGA94 coordinates derived from the ARGN. Network adjustments were required to obtain the best possible coordinates for control marks and photo control targets. Ausgeiod98 was used to model AHD elevations since no AHD benchmark was available. Network adjusted control marks agreed well with independent checks obtained from the online AUSPOS GPS data processing service. All network adjustment residuals satisfied the required accuracies.