Low cost, real-time GPS positional tracking on digital satellite images improves ground truth productivity

Field computers, palm-pilots and data storage devices are becoming smaller, more energy efficient and thus more practical to use in a wide variety of field data gathering scenarios. Validation of Earth observation (EO) data sets requires knowledge of greater positional precision as EO data resolution increases to metre and submetre scales. Software from a variety of commercial and public domain sources bridges the functionality gap that integrates stored digital images and real-time GPS data (with WAAS or subsequently corrected GPS-C technology). The software is currently user-friendly enough to allow for a seamless storage of positional field stop information linked with other instrument measurements or associated with georeferenced EO data in GIS databases. Examples presented here from several field campaigns indicate that in some cases, the increase in productivity was as high as 40-50%. This is especially true under cold weather conditions where freedom of movement, note taking and manual data recording are hampered. GPS positional information also allows several points or tracks to be collected in rapid succession, thus enabling two-dimensional information stops or area plots to be collected in addition to the traditional "point location". The locations of terrain features are often readily recognizable on digital imagery. This allows for immediate verification and confirmation of the site. GPS data collection is not limited to two-dimensions, and real-time 3D (altitude) information can guide the user along constant hypsometric levels in the field. In other cases, processed and georeferenced EO data may contain thematic information that does not correspond to visual image-like characteristics. Navigation from these kinds of imagery to their corresponding field locations may be difficult in these circumstances. Real-time positional displays, however, may help guide the field worker to the correct location on the imagery to be visited. In conclusion, field use of integrating GPS technology with EO data in real-time can greatly increase the efficiency of data collection campaigns as well as reduce errors and questionable data since it allows for an immediate visual feedback and validation by the user.