GNSS Interferometric Reflectometry

The goal of this web app is to measure the vertical distance (or reflector height RH) between the GNSS antenna and the horizontal surface (snow,water,soil) below the antenna. More details are available at this link.

The general principals of the GNSS-IR technique are shown here for a single GNSS signal. If a surface below a GNSS antenna is fairly planar, the reflected signal will be observed by the GNSS system. This effect is especially prominent at low satellite elevation angles. Each rising or setting satellite arc can potentially be used, which allows subdaily RH to be estimated if desired.

The reflections create oscillations in the GPS SNR data (top). The frequencies of these oscillations are estimated using a periodogram (below). Quality Control metrics include the required amplitude of the peak and how large the peak is relative to the periodogram values for a given RH range (i.e. 0.5 to 6 meters in this example).

Various examples of periodograms for "good sites"
  • Tides - St Michael in summer
  • Summit Camp, Greenland
  • Poster child for snow
  • Tides in Washington State,
  • Neem Camp, Greenland
  • Where it all began