Passive microwave sensor

The passive microwave sensor detects natural background microwave radiation. Oil slicks on water absorb some of this signal in proportion to their thickness. While this cannot be used to measure thickness absolutely, it can yield a measure of relative thickness. The advantage of this sensor is that it can detect oil through fog and in darkness. The disadvantages are the poor spatial resolution and relatively high cost. 

Fig. 5. Top left Laser-induced Raman backscatter (381 nm) and two fluorescence return signals (414, 482 nm) measured during an overflight over an oleyl alcohol slick and adjacent clean sea areas bottom left the simultaneously obtained passive microwave L-band data top right same lidar sensor, Raman backscatter (381 nm) and fluorescence return signal at 500 nm during an overflight over a Murban cmde oil spill and adjacent clean sea areas bottom right same passive microwave sensor, over an artificial oil spill in the New York Bight.

Dual-technology sensors consist of two different sensor technologies incorporated together into one sensor unit. For example, a dual technology sensor could consist of a passive infrared detector and a monostatic microwave sensor integrated into the same sensor unit. 

As can be inferred from Table 3, some remote sensors appear to bear a potential for the discrimination of sea slicks and crude oil spills. The most promising approach was published by Huhnerfuss et al. (1986) who showed evidence that both Lidar and passive microwave L-band sensors may be able to discriminate between slicks and spills (Figure 5). 

Refinement of methodologies to improve the reliability of the identification of oil spills (reduction of the false positives and false negatives rate). Possible research directions include the refinement of tools for the analysis of images acquired by a number of different sensors, such as RADAR, IR, UV, Passive Microwave, the fusion of information from different sensors as well as the integration of auxiliary data (meteo and oceanographic data). 

Holter, M. R. et al. 1970, Imaging with Non-Photographic Sensors [radar, passive microwave, infrared, visible, and ultraviolet], in Remote Sensing with Special References... (see NAS-NRC). 

Free-standing sensors—These sensors, which include active infrared, passive infrared, bistatic microwave, monostatic microwave, dual-technology, and video motion detection (VMD) sensors, consist of individual sensor units or components that can be set up in a variety of configurations to meet a user s needs. They are installed aboveground, and depending on how they are oriented relative to each other, they can be used to establish a protected perimeter or a protected space. More details on each of these sensor types are provided below. 

This topic merits separate treatment due to the novelty of the technology and wide variety of studies thus far the applications are primarily passive (unswitchable) camouflage in the microwave and far-IR regions, and sensors. 

---