OHB System has received a €554 million contract from the European Space Agency to lead development of Sentinel-3 Next Generation Topography, a dedicated radar-altimetry mission for Europe’s Copernicus Earth observation program. The November 4 announcement identifies OHB as prime contractor for a European industrial consortium and includes an option for a second satellite.
The planned mission uses two identical spacecraft in sun-synchronous orbit to measure oceans, coastal waters, sea ice, and inland waters. Its design separates radar measurements from the optical observations carried together on the existing Sentinel-3 satellites. The next-generation topography spacecraft will concentrate on surface-height measurements, with planned improvements in precision, coverage, and revisit frequency.
Measuring Height From Orbit
A radar altimeter measures distance by transmitting pulses toward Earth and timing their return. Combining that distance with the satellite’s precisely determined orbital position yields the height of the reflecting surface. ESA’s radar-altimetry explanation describes measurements collected along the spacecraft’s ground track, rather than a conventional photographic image.
Over the ocean, repeated height measurements reveal changes in the sea surface. Over inland waters, the same underlying measurement principle supports observations of lake and river levels. The surface being observed and the characteristics of its radar reflection determine how the returning signal is interpreted.
The existing Sentinel-3 instrument package combines a synthetic aperture radar altimeter with optical instruments that measure surface temperature and color. Its radar operates at Ku- and C-band frequencies, and a microwave radiometer supplies information used to correct atmospheric effects on the measurements.
These instruments perform different jobs. Optical measurements describe properties such as ocean color and temperature; radar altimetry establishes height and related surface information. New Space Economy’s account of Sentinel-3 height measurements explains the supporting role of precise orbit determination alongside the radar observations.
The new contract advances a mission architecture dedicated to the topography part of that work. OHB will coordinate the consortium developing the spacecraft, with the second satellite remaining an option within the announced contractual arrangement.
