Ground-Truthing

Geology is the study of the earth; however programs such as GIS have allowed geology data collection to move indoors. If you’ve followed my posts you know that my research relies heavily on the data available for use in GIS and the analyses which can be done in the program. In order to do this we needed to determine how closely results from GIS match what’s actually happening on our fields. As I mentioned in the previous post, our task this week was to ground-truth our channel locations. Tuesday this week, a teammate and I visited the cotton-planted field surrounding Peace Hill Bed & Breakfast in Charles City County. Using a GPS unit, aerial photography and a topo map we walked the perimeter of the field marking locations of concentrated flow.

These locations were determined by looking for specific evidence of flow such as incising of the ground, leaf and sediment movement, as well as holes from ground water sapping. These channels were classified into 4 classes, with 1 being lower flow levels and 4 being the highest. This will allow us to compare the flow accumulation values to in-field flow evidence. Once an incised channel was located we followed the channel off the field and into the woods towards the nearby buffer/stream system. Our project is investigating channel incision which leads to buffer bypassing and knowing whether the channel reaches the stream is an important step in determining the extent of the bypassing dilemma. The GPS points have not yet been loaded into ArcMap, however it was clear that actual flow evidence in the field occurred in points near the predicted locations in GIS. After more fields have been walked I will analyze the relationship in depth.

Ground truthing will be the focus for much of the last few weeks of summer, yet I still continue to work on delineations of fields in the Coastal Plain weekly. This week I completed 10 fields in New Kent County, each with 10m DEMs from the Seamless server. This brings the total to 23 fields, 4 of which were done in LIDAR as well as the 10m sets. The next focus of GIS field delineations will be James City County. The county is available in new 1.5m LIDAR so I hope to use these data sets for each field. I also plan to ground-truth several of these fields as well to be sure results are similar regardless of the data resolution.