D1 Satellite Remote Sensing

Topic

Satellite remote sensing measures cryospheric properties from Earth-orbiting platforms by emitting or receiving electromagnetic signals across various spectral bands to characterize ice from space. It is the only method offering truly global, temporally repeated, and spatially consistent coverage; this type of coverage is essential for monitoring changes in ice extent, glacier volume, and the mass balance of the cryosphere as a whole.

Two satellite remote sensing techniques measure ice surface elevation from orbit: a laser altimetry mission measures the distance between the satellite and the ice surface by timing the flight of laser light pulses, with the difference in measured distance between successive satellite passes revealing the change in ice thickness over time. In contrast, a radar altimetry mission transmits a signal that partially penetrates dry snow before reflecting; consequently, the elevation measured corresponds to a scattering surface located slightly below the visible ice surface.

A satellite gravimetry mission operates on a different principle: it detects variations in Earth's gravitational field caused by the ice mass itself. When the ice loses mass, the local gravitational field weakens—a change measurable from orbit—and the mission translates this weakening directly into a change in ice mass, without needing to first assume a specific ratio of ice thickness to elevation, as altimetry missions must do. A passive microwave sensor measures the natural microwave emission radiated by the sea ice itself; the microwave emission captured by this sensor allows for the calculation of both sea ice concentration and extent over the ocean during each satellite pass.

An interferometric radar technique combines the phases of multiple radar images captured from space over the same location at different times; this combination of phases between successive images enables the calculation of ice surface displacements with millimeter-level precision.

When integrating all these independent techniques, the expected outcome of satellite remote sensing is that they all detect the same trends—thinning, mass loss, and reduced ice extent. This consistency across independent methods is precisely what allows the observed changes in the cryosphere to be attributed with a high degree of confidence, thereby underscoring the essential role of satellite remote sensing as the only tool capable of monitoring Earth's entire cryosphere with the global, repeated, and consistent coverage described at the outset.

ID:2658