SCM x330 Ocean Discovery through Technology Area F GE

Platforms - Satellites Passive Satellites: AVHRR Ocean Color Salinity Active Satellites: (RADAR) Altimetry SAR Theory Application Sensor

Passive remote sensing systems record electromagnetic energy that is reflected (e.g., blue, green, red, and near- infrared light) or emitted (e.g., thermal infrared energy) from the surface of the Earth. There are also active remote sensing systems that are not dependent on the Sun’s electromagnetic energy or the thermal properties of the Earth. Active remote sensors create their own electromagnetic energy that 1) is transmitted from the sensor toward the terrain (and is largely unaffected by the atmosphere), 2) interacts with the terrain producing a backscatter of energy, and 3) is recorded by the remote sensor’s receiver.

Remote Sensor Resolution Spatial - the size of the field-of-view, e.g. 10 x 10 m. Spectral - the number and size of spectral regions the sensor records data in, e.g. blue, green, red, near-infrared thermal infrared, microwave (radar). Temporal - how often the sensor acquires data, e.g. every 30 days. Radiometric - the sensitivity of detectors to small differences in electromagnetic energy. 10 m BGRNIR Jan15Feb m

Advanced Very High Resolution Radiometer - AVHRR The AVHRR is a radiation-detection imager that can be used for remotely determining cloud cover and the surface temperature. Note that the term surface can mean the surface of the Earth, the upper surfaces of clouds, or the surface of a body of water. This scanning radiometer uses 6 detectors that collect different bands of radiation wavelengths as shown below. The first AVHRR was a 4-channel radiometer, first carried on TIROS-N (launched October 1978). This was subsequently improved to a 5-channel instrument (AVHRR/2) that was initially carried on NOAA-7 (launched June 1981). The latest instrument version is AVHRR/3, with 6 channels, first carried on NOAA-15 launched in May 1998.

Ocean Color

Sea-viewing Wide Field-of-view Sensor (SeaWiFS)

Airborne L-Band Salinity Mapping Radiometer System The Airborne L-Band Radiometer Mapping System was developed by ProSensing along with research scientists from NRL and NOAA. The system includes two radiometers: a Scanning Low Frequency Microwave Radiometer (SLFMR) that detects changes in both ocean surface temperature and salinity and a dual-channel infrared radiometer that provides a direct measurement of the ocean surface temperature. The output of these instruments is combined to estimate sea surface salinity with an accuracy of 2-3 parts per thousand (ppt). The latest version of SLFMR, termed STARRS (Salinity Temperature and Roughness Remote Scanner) uses six independent 1.4 GHz Hach radiometer channels to simultaneously generate six cross-track beams. The STARRS system also includes a Stepped Frequency Radiometer (SFMR) that corrects for changes in brightness temperature due to ocean surface roughness. The resultant accuracy is estimated to be better than 1 ppt.

Why Radar? A satellite altimeter is a nadir pointing active microwave sensor designed to measure characteristics of the surface of the Earth. The return signals from ocean regions provide information on significant wave height, surface wind speed and a range measurement from the satellite to the sea surface immediately below. A radar altimeter operates by timing the delay between emission of a short microwave pulse and the subsequent detection of the returned echo, recording the time and distortion of the returned signal. The operation of all altimeters is broadly similar and, unless explicitly stated otherwise, we describe the operation and characteristics of a typical Ku-band satellite radar altimeter (approx 13 GHz). The first requirement for any remote sensing instrument wishing to observe the Earth's surface is that atmospheric attenuation of the electromagnetic signal be sufficiently small that detection of the return pulse is possible. Through most of the infra-red region, signal attenuation is large due to atmospheric water vapor and gases such as carbon dioxide and oxygen. In the microwave region between 100 MHz and MHz, however, signal attenuation is small.

Ocean topography missions like TOPEX/Poseidon and Jason-1 seek to satisfy the following science goals: To determine general ocean circulation, and to understand its role in the Earth's climate, and its hydrological and biogeochemical cycles. To study the variation of ocean circulation on time scales from seasonal and annual to decadal and the effects on climate change. To collaborate with other global ocean monitoring programs to produce routine models of the global ocean for scientific and operational applications. To study large-scale ocean tides. To study geophysical processes from their effects on ocean surface topography. Gravity, bathymetry, and mesoscale ocean circulation from altimetry

The term synthetic aperture radar (SAR) describes a way of synthesizing a very large array antenna over a finite period of time by using a series of returns from a much smaller physical antenna that is moving relative to the target. By synthesizing a large array, the synthetic aperture radar (SAR) can enjoy the benefits of improved angular resolution that come with large antennas without the problems associated with large antennas. In fact, we see that much larger synthetic apertures can be formed than would be possible using a real antenna. SAR

Applications