Remote Sensing of Permafrost
Active Microwave Sensing
NSCAT
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The NASA Scatterometer (NSCAT) was launched aboard the Japanese satellite Midori, also known as the Advanced Earth Observing Satellite (ADEOS), on August 16, 1996. The unfortunate premature power failure of the ADEOS spacecraft resulted in a termination of the NSCAT mission on June 30, 1997. While in operation, NSCAT provided approximately 70% global ice-free ocean coverage every day with a measurement footprint of 25 km. Nearly 10 months of continuous global ocean surface wind vector data was provided by NSCAT, representing an unprecedented achievement by NASA.
NSCAT used eight antenna beams to scan two wide bands of ocean, one on each side of the instrument's orbital path. NSCAT transmited short pulses of microwave energy to probe ocean surfaces and then measured the reflected or backscattered power.
Source: NASA
ERS-1 Satellite and SAR imaging
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In 1991, ESA launched the first European Remote Sensing satellite, ERS 1, and started building a catalogue of interferometric data covering the whole Earth. ERS 2 was launched in 1995, to continue and expand the work. The image pairs acquired provide much greater interferogram coherence than is normally possible, allowing scientists to generate detailed digital elevation maps and observe changes over a very short space of time.
Synthetic Aperture Radar (SAR) is a microwave imaging system. It has cloud penetrating capabilities because it uses microwaves; it has day and night operational capabilities because it is an active system; and its ‘interferometric configuration’, Interferometric SAR or InSAR, allows accurate measurements of the radiation travel path because it is coherent. Measurements of travel path variations as a function of the satellite position and time of acquisition allow generation of digital elevation models and measurement of centimetric surface deformations of the terrain.
Source: ESA
Active sensors use stimuli sent from the sensor to collect data about Earth. For example, a laser-beam remote sensing system projects a laser onto the surface of Earth and measures the time that it takes for the laser to reflect back to its sensor.
Source: NOAA