mapping bed topography

Today was a busy day. Brian came down to help, so we had a total of six people. We split up into three groups to run (1) the ground-penetrating radar (GPR), (2) the laser scanner, and (3) the precise point kinematic (PPK) GPS to record stake location.

We are using a long snake 25 MHz GPR to record bed topography of the lower glacier. We hope that this frequency will be sufficient to see the ice-bed interface, despite the water-saturated ice and bed interface. Bed topography is important for this study because it is one of the variables that determines how and where water will be routed underneath the glacier, as well as how the ice flows.

Brian and Karen drag the GPR across the glacier

In addition to running the GPR, we also used the PPK GPS for the first time today. We are using the PPK GPS every other day to determine velocity rates at our ablation stakes. This setup differs from a typical handheld GPS in that we can get far more precise locations. With a handheld GPS, the typical accuracy is about 5-7 m in the horizontal and 10+ m in the vertical, depending on the number of satellites. With a PPK setup, we can get down to millimeter accuracy. This is partially because we use a base station in addition to a roving unit. As the base station remains in one known location, any changes in it's location over the study period can be attributed to changes in the atmosphere and travel time of the GPS signal. This allows us to make atmospheric corrections at the end and retrieve much more accurate results depending on how long we remain at a given stake, the number and arrangement of satellites, etc.

The last group, which included Martina and I, used the laser scanner to determine glacier topography. Today's scanning was far more successful than the day before, and tomorrow should be our last day of scanning.

Laser scanning