NASA's Aquarius Launched To Help Map the Oceans' Salt 64
oxide7 writes "NASA launched a satellite featuring an brand-new instrument which will be able to measure the saltiness of Earth's oceans. Data from the Aquarius/SAC-D spacecraft will help scientists understand better the processes that drive ocean circulation and the movement of freshwater around the planet."
Re:Mechanism? (Score:2, Informative)
Salinity and temperature are the only things that alter the energies emitted and reflected by the ocean at certain centimetre wavelengths (frequency, 1.43 GHz). The atmosphere is almost transparent - no pesky gas, cloud or mostly rain. After that, you've got to model the galactic radiation which is also reflected and causes a lot of problems- luckily it's well known as it doesn't alter quickly very often.
BTW, the NASA Aquarius web site talks sheer nonsense that this is first salinity satellite. SMOS, launched by ESA, has been mapping the seas for a year or more.
Re:Mechanism? (Score:2, Informative)
http://oceancolor.gsfc.nasa.gov/WIKI/AQ(2f)GS(2f)AquariusInstrumentDescription.html
The instrument is a kind of radar called a scatterometer. It measures the amount of L-band (1400 MHz-ish) power reflected back by the ocean's surface. If you compare the amount scattered back in Horizontal and Vertical polarization, you can tell the dielectric properties of the water (mostly conductivity changes). In general, the reflection in vertical polarization (perpendicular to the surface) is more strongly affected by epsilon (dielectric constant) than horizontal pol, and both change with angle of incidence. (why polarized sunglasses help looking into water, block the Hpol and you get rid of most of the reflection)
The challenge is in measuring the very small changes, so the instrument has a variety of schemes to calibrate out changes in transmitter power, atmospheric losses, receiver gain, etc. (not to mention that the sea surface roughness has an effect.. a frosted window reflects a different amount of light than a shiny smooth one).
For EE geeks, think of an instrument like this as flying a VNA with a measurement uncertainty 0.1dB.