PRETTY

Project title

Passive REflectomeTry and DosimeTrY

Goal

Exploit GNSS reflectometry data for Earth Observations over the global oceans and polar areas

Period

2023 -

Funded by

Beyond Gravity Austria (BGA), European Space Agency (ESA)

Project lead

Norwegian University for Science and Technology (NTNU)

Reference

ESA

The PRETTY satellite mission (Passive REflectomeTry and DosimeTrY) is a three-unit cubesat that was launched from French Guiana on October 9th, 2023 into a low Earth orbit (~560km altitude). The main payload is a passive reflectometer that collects data of Earth-reflected signals transmitted by GNSS (Global Navigation Satellite System) constellations, in particular Galileo and GPS. The mission goal is to exploit GNSS reflectometry data for Earth Observations over the global oceans and polar areas. A focus lies on sea surface and sea ice altimetry as well as on the atmospheric impact induced by ionospheric and tropospheric refraction of the signals.

Other satellite missions for GNSS reflectometry have been lauched before (e.g. TDS-1 and CyGNSS). However, PRETTY is the first dedicated mission to demonstrate the capabilities of GNSS reflectometry in grazing geometry. In contrast to near-nadir geometries where radar signals are received with small incidence angles, the grazing geometry corresponds to signal incidence close to the Earth limb. In grazing geometry the Earth-reflected signals are less affected by surface roughness and higher signal amplitudes are achieved compared to near-nadir geometries. Also, the Earth surface coverage of the reflectometer is larger in this case. Challenges in grazing geometries arise from gradually reduced sensitivity of the reflected signal to the reflecting surface height and from longer path lengths in the Earth's atmosphere that increase refraction effects. Both challenges are particularly important for altimetry (surface height retrieval) and major fields of research in this demonstrator mission.

A science team has been formed for the PRETTY mission with partners from Germany, Norway and Spain. The task of the DLR-SO team is to model refraction effects introduced by the ionosphere and to investigate the impact of related delay uncertainties on altimetric results. Additionally, the PRETTY mission offers a unique opportunity to explore retrievals of ionospheric parameters (electron content, layer peak height) using grazing angle observation data.

Additionally to DLR-SO, the following institutes are involved:

  • Norwegian University for Science and Technology (NTNU), Trondheim, Norway
  • German Research Center for Geosciences (GFZ), Potsdam, Germany
  • Institute for Space Studies Catalunya (IEEC), Barcelona, Spain