Passive Microwaves

Only a limited amount of observations have been recorded in the passive hyper frequencies however, we can already propose some principles of observation. 

First principle. Based on the tremendous variations in emissivity values, linked to water, humidity, moisture, day or night, under a cloudy or clear sky. The average emissivity is around 0.4 for water, but this value increases when the water temperature decreases and vice versa. When an object is wet, its brightness temperature immediately drops very sharply. Looking at two identical soils, one dry, the other slightly wet, the latter shows a much lower than the first. Finally foreign bodies poured into water (dust and /or chemicals) provoke a sharp emissivity increase. 

Second principle. Contacts between different rock formations are sharply emphasized, due to the emissivity differences. One sees the geological facilities helping with geological maps one sees too, how tectonic accidents could be easily detected, the difference in emissivity between rock formations on either side of the lips (fault line) being boosted by water joints and faults are sites favored by the migrant humidity. 

Third principle, linked to recognition of soil formations. This principle is the same as for rock formation, but it goes farther the moisture of different soils and that between different soil horizons shows up with much lower brightness temperatures. The passive microwaves are ideal for the remote detection of the most insidious type of soil erosion, namely sheet erosion. 

Fourth principle. All man-made constructions, buildings, highways, factories, etc. considerably reduce emissivity. 

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Josephson junctions for passive microwave devices, satellite-communication systems, and computer logic gates. 

Shuman, C. A., Alley, R. B., Anandakrishnan, S. et al. (1995). Temperature and accumulation at the Greenland Summit Comparison of high-resolution isotope profiles and passive microwave brightness temperature trends. /. Geophys. Res. 100(D5), 9165-9177. 

Lorenz, M. Hochmuth, H. Natusch, D. Lippold, G. Svetchnikov, V. L. Kaiser, T. Hein, M. A. Schwab, R. Heidinger, R. 1999. Ag-doped double-sided PLD-YBCO thin films for passive microwave devices in future communication systems. IEEE Trans. Appl. Supercond. 9 1936-1939. 

Microwave temperature profiler passive microwave radiometry of 02 thermal emission 35... 

Sippel, S. J., S. K. Hamilton, J. M. Melack, and E. M. M. Novo. 1998. "Passive microwave observations of inundation area and the area/stage relation in the Amazon River floodplain." International Journal of Remote Sensing, 19 3055-3074. 

A passive microwave reflector needs little maintenance and requires no power. Their principle drawback... 

Among the most commonly used algorithms for estimation of ice concentration from passive microwave data (such as SMMR and SSM/1) are the NASA Team and Bootstrap algorithms [22-24]. These algorithms use various combinations of TB data from various polarisations (H or V) and various frequencies (19 or 37), such as the polarisation (PR) and spectral (GR) gradient ratios. For Arctic and Antarctic tie points for open water, first-year and multi-year ice has been identified and based on them estimation of both ice cmicentration and type are possible [24,25]. 

Cavalieri DJ, Parkinson CL, Gloersen P, Comiso JC, Zwally HJ (1999) Deriving long-term time series of sea ice cover from satellite passive-microwave multisensor data sets. J Geophys Res 104(C7) 15803-15814... 

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. 

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). 

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.

With regard to the Lidar measurements, the presence of an OLA slick at the ocean surface caused a decrease in both the Raman backscatter at 381 nm and of the fluorescent bands at 414 and 482 nm, while in the presence of a thick cmde oil spill the Raman depression at 381 nm was accompanied by a simultaneous increase in the longer wavelength bands. During the same overflights a dramatic decrease in the passive microwave L-band signals was observed in the presence of an OLA slick (Blume et al. 1983), while in the presence of a cmde oil spill an increase in the same band is encountered. Unfortunately, a verification of the latter conclusions is still... 

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). 

Shuman CA, Alley RB, Anandakrishnan S, White JWC, Grootes PM, Steams CR (1995) Temperature and accumulation at the Greenland Summit comparison of high-resolution isotope profiles and satellite passive microwave brightness temperature trends. J Geophys Res 100 9165-9177 Sowers T, Bender ML, Raynaud D (1989) Elemental and isotopic composition of occluded O2 and N2 in polar ice. J Geophys Res 94 5137-5150... 

Specific properties of superconductors at 77 K may be used for electronic applications, e.g., for passive microwave devices such as transmission lines and high-quality resonators. YBCO is widely used in active devices such as SQUIDs and detectors based on Joseph-son and quasi-particle tunnelling. A further field of... 

FIGURE 4.21 Incident, reflected, and transmitted traveling voltage waves at (a) A passive microwave element, (b) a transmission line. 

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