Prototype Experiment

The purpose of the prototype experiment is to collect test data to validate the geodedic technique. The test is to be conducted at a site on an ice sheet that has previoulsy been mapped with ground-penetrating radar, so that the depth to the basal reflector is known.

Monstatic (Vertical Incidence) Tests: The transmiting and receiving antennas are colocated.

1. Signal to Noise Test: The antenna is placed at a single site, and a variety of different carrier frequencies (50 MHz - 1 GHz) are used. The data are used to understand the length of time needed to achieve a 10:1 signal-to-noise ratio.
   • Can firn reverberations be recognized?
   • Can the basal reflector be recognized?
   • Can velocity dispersion be measured?
2. Antenna Placement Repeatability Test: The antenna is removed from the site and then re-emplace, with every attempt made to completely duplicate its original position. The data are used to estimate the loss of coherence associated with antenna re-emplacement.
   • Is antenna coupling a problem?
   • If so, what field techniques can be used to minimize this problem?
3. Spatial Coherence Test: Data is collected, the antenna is moved a distance, dx, and data are collected again. A variety of dx's, in the 1-1000 m interval, are used to estimate the spatial coherence of the signal.
   • Is the basal reflection more coherent than the firn reflections?
   • Does the data suggest that the coherence is being controlled by scatters in the firn (or elsewhere)?
4. Firn Disturbance Test: Data is collected, the antenna is removed, the firn is disturbed (compacted) by "steamrolling", and then the antenna re-emplaced and a comparison data set is collected.
   • How well can the change in the firn be determined?
   • How large is the error in dterming the change in basal reflector depth (which should be exactly zero).
5. Internal Standard Test: A metal cylinder a few cm in diameter is emplaced in the firn at a depth of a few meters (via a borehole). The antenna is operated a few meters away.
   • Do diffractions from the cylinder provide a useful reference signal that can be used as an "internal standard" to reduce re-emplacement errors?
   • How far from the antenna should the cylinder be?
6. Polarization Test: Data is collected with the transmitter sending out a "north" polarization, and the receiver listing to first "north" and then "east" polarizations. The measurements are repeated, but with the transmitter sending out an "east" polarization. The measurements are repeated at a variety of different carrier frequencies.
   • Can dielectric anisotropy be detected?
   • If so, in what depth ranges is it the most important?

Bistatic (Wide-angle) Tests: The transmitting and receiving antennas are separated by 9000-10000 m.

1. Timing Stability Test: Atomic clocks are used to measure the GPS-timing stability under actual Arctic field conditions.
2. Basal Reflector Coherence Test: Data is acquired for several transmitter-receiver offsets, with the transmitter at a fixed location and the receiver in the 9+dx range, with dx varying from 1-1000 m interval. The receiver locations should be the same as in the monstatic test, above, to allow comparison with vertical incidence data.
   • How coherent is the basal reflector?
   • Does the data suggest that the coherence is being controlled by scatters in the firn or on the basal surface?
3. Traveltime Variability Test: The data from the previous test are used to estimate basal reflector traveltime as a function of range.
   • How smooth is this traveltime curve?
   • Can small-scale features be accounted for by changes in firn structure?