Invited Paper

Fluctuations in millimeter -wave signals caused by clear -air turbulence and inclement weather

R.J. Hill,' R.A. Bohlander,2 S.F. Clifford,' R.W. McMillan,2 and R.J. Lataitis'

ABSTRACT

Observations and theory for millimeter -wave propagation through clear -air turbulence, rain, fog, and snow arereviewed. Measurements have shown the effects of refractive and absorptive fluctuation in air. Measured quantitiesinclude the intensity, the phase difference between spaced antennas for a single electromagnetic frequency as well asplease difference at a single antenna for waves having differing frequencies. Typical statistics of these quantities aretheir variances, structure functions, temporal spectra, and probability distributions.

I. INTRODUCTION

Experiments on the effects of clear -air turbulence on millimeter -wave (mm -wave) propagation have investigatedthe effects of refraction and absorption fluctuations on intensity and phase -difference spectra and variances, prob-ability densities of intensity and phase difference, the coherence of waves of different wavelength propagated simul-taneously, the effect of the outer scale of turbulence on intensity statistics, measurement of cross -path wind compo-nent and refractive structure constant from intensity scintillation, and the use of the simultaneous scintillation ofoptical and millimeter waves to measure the surface fluxes of heat and humidity.' -48 Clear -air propagation theoryhas been developed49 - 72 for the effects of refraction and absorption fluctuations on intensity and phase variances,spatial and temporal spectra, beam wave propagation, and the applicability of small -angle forward scattering.

There remain theoretical challenges. The intensity at a single antenna is a commonly measured quantity. Theeffect of absorption fluctuations on intensity is analogous to the effect of refraction fluctuations on the total phase(i.e., the number of wavelengths from the transmitter to the receiver). The intensity and total phase are thennonstationary random variables and are particularly sensitive to meteorological variability of the largest time andspace scales. This nonstationarity has never been adequately treated. Also, because of this sensitivity to large spatialscales, the "Markov approximation" (that the largest scale of randomness is much smaller than the propagationpath length) must he removed; this can he accomplished at the expense of computing higher -order integrals for thepropagation statistics; this is a significant complication. Millimeter -wave statistics have a significant influence fromthe outer scale of turbulence; this is true even for phase- difference statistics (and therefore for angle -of- arrivalstatistics). Therefore, the true anisotropic refractive -index spectrum at low spatial wavenumbers is needed, ratherthan the isotropic, idealized von Karman spectrum. This requires yet an additional numerical integration to calculatepropagation statistics. However, the true anisotropic spectrum is not known; although there is some empirical evi-dence, the spectrum at low wavenumbers is highly variable.

2. THE EXPERIMENT AT FLATVILLE

We performed a propagation experiment over exceptionally flat farm land near Flatville, Illinois.16, 73, 74 Exten-sive micrometeorological (hereafter abbreviated as micromet) measurements were made simultaneously. Because ofthe excellent horizontal homogeneity of the site, these micromet data determine the turbulence statistics along theentire propagation path. There were five experiment sessions, each about a month in duration. Several mm -wavefrequencies were used. instrumentation for measurements of rain as well as fog and snow were deployed. Results fordata during inclement weather were reported in Refs. 74 -76.

Figure 1 shows the experiment layout. The mm -wave beam propagated a distance of 1374 m at a uniform heightof 3.68 m j 0.1 m from the transmitter van to the receiver antennas. The separations of the receiving antennasranged from 1.43 to 10 m. The mm -wave intensity was measured at each of the four antennas, and the phasedifference between antennas was obtained for each antenna pair. The two overlapping optical propagation paths inFig. 1 were 670 m each at a height of 3.78 m. These gave the path- averaged optical refractive -index structureparameter (C,h,) as well as the cross -path component of the wind.

Instrumented towers denoted as meteorological stations 1 and 2 (met. sta. 1 and 2) are shown in Fig. 1. Atthese stations the mean temperature and humidity were recorded, a propellor -vane anemometer gave wind speedand direction, a three -axis sonic anemometer gave the fluctuating components of the wind vector, platinum resis-tance -wire thermometers gave the fluctuating temperature, and Lyman -a hygrometers recorded the humidity fluc-tuations.

' NOAA /ERL /Wave Propagation Laboratory, 325 Broadway, Boulder, CO 80303.

2 Georgia Technical Research Institute, Atlanta, GA 30332.

234 / SPIE Vol. 1115 Propagation Engineering (1989)

Invited Paper

Fluctuations in millimeter-wave signals caused by clear-air turbulence and inclement weather

R.J. Hill, 1 R.A. Bohlander, 2 S.F. Clifford, 1 R.W. McMillan,2 and R.J. Lataitis 1

ABSTRACT

Observations and theory for millimeter-wave propagation through clear-air turbulence, rain, fog, and snow are reviewed. Measurements have shown the effects of refractive and absorptive fluctuation in air. Measured quantities include the intensity, the phase difference between spaced antennas for a single electromagnetic frequency as well as phase difference at a single antenna for waves having differing frequencies. Typical statistics of these quantities are their variances, structure functions, temporal spectra, and probability distributions.

1. INTRODUCTION

Experiments on the effects of clear-air turbulence on millimeter-wave (mm-wave) propagation have investigated the effects of refraction and absorption fluctuations on intensity and phase-difference spectra and variances, prob­ ability densities of intensity and phase difference, the coherence of waves of different wavelength propagated simul­ taneously, the effect of the outer scale of turbulence on intensity statistics, measurement of cross-path wind compo­ nent and refractive structure constant from intensity scintillation, and the use of the simultaneous scintillation of optical and millimeter waves to measure the surface fluxes of heat and humidity. ~ Clear-air propagation theory has been developed ~ for the effects of refraction and absorption fluctuations on intensity and phase variances, spatial and temporal spectra, beam wave propagation, and the applicability of small-angle forward scattering.

There remain theoretical challenges. The intensity at a single antenna is a commonly measured quantity. The effect of absorption fluctuations on intensity is analogous to the effect of refraction fluctuations on the total phase (i.e., the number of wavelengths from the transmitter to the receiver). The intensity and total phase are then nonstationary random variables and are particularly sensitive to meteorological variability of the largest time and space scales. This nonstationarity has never been adequately treated. Also, because of this sensitivity to large spatial scales, the "Markov approximation" (that the largest scale of randomness is much smaller than the propagation path length) must be removed; this can be accomplished at the expense of computing higher-order integrals for the propagation statistics; this is a significant complication. Millimeter-wave statistics have a significant influence from the outer scale of turbulence; this is true even for phase-difference statistics (and therefore for angle-of-arrival statistics). Therefore, the true anisotropic refractive-index spectrum at low spatial wavenumbers is needed, rather than the isotropic, idealized von Karman spectrum. This requires yet an additional numerical integration to calculate propagation statistics. However, the true anisotropic spectrum is not known; although there is some empirical evi­ dence, the spectrum at low wavenumbers is highly variable.

2. THE EXPERIMENT AT FLATVILLE

We performed a propagation experiment over exceptionally flat farm land near Flatville, Illinois. '' ' Exten­ sive micrometeorological (hereafter abbreviated as micromet) measurements were made simultaneously. Because of the excellent horizontal homogeneity of the site, these micromet data determine the turbulence statistics along the entire propagation path. There were five experiment sessions, each about a month in duration. Several mm-wave frequencies were used. Instrumentation for measurements of rain as well as fog and snow were deployed. Results for data during inclement weather were reported in Rets. 74-76.

Figure 1 shows the experiment layout. The mm-wave beam propagated a distance of 1374 m at a uniform height of 3.68 m ± 0.1 m from the transmitter van to the receiver antennas. The separations of the receiving antennas ranged from 1.43 to 10 m. The mm-wave intensity was measured at each of the four antennas, and the phase difference between antennas was obtained for each antenna pair. The two overlapping optical propagation paths in Fig. I were 670 m each at a height of 3.78 m. These gave the path-averaged optical refractive-index structure parameter (Cn) as well as the cross-path component of the wind.

Instrumented towers denoted as meteorological stations 1 and 2 (met. sta. 1 and 2) are shown in Fig. 1. At these stations the mean temperature and humidity were recorded, a propellor-vane anemometer gave wind speed and direction, a three-axis sonic anemometer gave the fluctuating components of the wind vector, platinum resis­ tance-wire thermometers gave the fluctuating temperature, and Lyman-c* hygrometers recorded the humidity fluc­ tuations.

1 NOAA/ERL/Wave Propagation Laboratory, 325 Broadway, Boulder, CO 80303.

2 Georgia Technical Research Institute, Atlanta, GA 30332.

234 / SPIE Vol. 1115 Propagation Engineering (1989)

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/01/2013 Terms of Use: http://spiedl.org/terms

3. MILLIMETER -WAVE RESULTS FROM FLATVILLE

A summary of mm -wave propagation statistics froni tapes 20 and 24 is given in Table 1: these tapes correspondrespectively to radio refractive -index structure parameter values of 1.9 and 6.2 x 10-12 m -2". The absolute mm-wave intensity (in say W /m2) is not measured. All intensity statistics are of the intensity divided by its mean value;thus the intensity statistics are dimensionless. Ideally the intensity statistics at all four antennas should be equal. 'Thephase- difference statistics are in radian units. As expected, the phase -difference variances increase with increasingantenna separation. The minimum and maximum observed phase differences during these data runs had changes aslarge as tTr.

Figure 2 shows an intensity probability density function (PDF). Gaussian and lognormal PDFs having the samemean and variance are also plotted. There is little difference between the Gaussian and lognormal PDFs for suchsmall values of variance. However, the data are clearly skewed and more nearly follow the lognormal PDF, as isexpected theoretically, provided that the effects of absorption fluctuations are negligible. When absorption fluctua-tions substantially influence the intensity variance, then the lognormal PDF is not observed.

Figure 3 shows the phase -difference PDF from antennas 2 and 3 of session 1, tape 24. A Gaussian PDF havingthe sanie mean and variance is also plotted. Clearly the phase difference is Gaussian, as is expected theoretically.

Figure 4 shows the structure function of phase versus receiver separation. The six receiver separations corre-spond to the six antenna pairs. At a given receiver separation, the value of the structure function of phase is just thephase- difference variance for the corresponding antenna pair. Also plotted is a theoretical prediction for the 6:50p.m. data using the micromet -value of Cñ and assuming a 2.2 -m outer scale and a von Karman refractive -indexspectrum. Using a 2.2 -m outer scale produces a theoretical structure function of phase having nearly the sameshape as the data.

Figure 5 shows the normalized intensity variance plotted versus the theoretical formula for a spherical wavepropagating through inertial -range turbulence. Here, C; is deduced from the micromet data. Data agreeing perfectlywith theory would lie on the straight line. The slight (- 12%) lack of agreement could be caused by the outer scaleof turbulence and possibly by inaccurate calibration of the Lyman -a hygrometer.

Figure 6 contains a log -log plot of (f /fe) times the log -amplitude spectrum WX versus normalized frequency(f /f ). The spectrum WX is normalized to the log -amplitude variance such that the area under the curve is unity. Thefrequency f = v /I2 rAL, where v is the cross -path component of windspeed, X is the wavelength, and L - 1.4 km isthe millimeter -wave path length. The dotted (solid) fluctuating curve represents the low (high) frequency Fouriertransform of 35 min of log -amplitude data taken at 142 GHz. The solid theory curve fits the data quite well until thehigh frequency tail beyond log ( % /f) = I. where aperture averaging effects are important. The dashed curve is a plotof the theory including aperture averaging effects; overall, the fit to the data is excellent. Deviations at low frequen-cies above the "theory curve are most likely due to receiver drift. It is possible from the theory to estimate thecross -path velocity from the location of the peak. The peak is predicted at log (f /f) - 0.43. In the case shown. thecross -path velocity estimate from the millimeter wave scintillations agrees with the propellor -vane anemometer data.

Figure 7 shows a measured log -amplitude spectrum as a function of temporal frequency in Hz. The high -fre-quency part above 0.5 Hz is similar to the result in Fig. 6; this part of the spectrum is dominated by refractionfluctuations and is amenable to traditional theory. The low -frequency part in Fig. 7 is caused by an absorption eventduring the run; specifically, the humidity increased along the entire path during the run. Although we have a theoryapplicable to absorption fluctuations of scale much smaller than the path length, the event resulting in the spectrumin Fig. 7 is not described by existing theory. Such an event produces an intensity PDF that is not lognormal.Obviously from Fig. 7, this absorption event produced most of the intensity variance, violating the assumptions thatproduce agreement in Figs. 5 and 6.

Figures 8 and 9 show theoretical curves superimposed over the phase -difference spectra from the data forantenna pair (I,2) separated by Q12 = 1.43 m and antenna pair (1,4) separated by pt4 = 10 m. We used the valueL - 2.8 m and selected our curves to fit the data based on the ratios et2 /L = 0.5 I and X14 /L = 3.5 appropriateto each antenna pair. The resulting fit is quite good. We could also-estimate crosswind from the peak of the spec-trum if we knew the accurate L from other independent measurements.

ACKNOWLEDGMENT

The research was supported in part by the U.S. Army Research Office under Contracts DAAG29 -81 -K -0173,DAAG29 -77 -C -0026 and M I PR 122 -85.

SPIE Vol 1115 Propagation Engineering (1989) / 235

3. MILLIMETER-WAVE RESULTS FROM FLATV1LLE

A summary of mm-wave propagation statistics from tapes 20 and 24 is given in Table 1: these tapes correspond respectively to radio refractive-index structure parameter values of 1.9 and 6.2 x 10~ 12 m~ 2/3 . The absolute mm- wave intensity (in say W/m 2 ) is not measured. All intensity statistics are of the intensity divided by its mean value; thus the intensity statistics are dimensionless. Ideally the intensity statistics at all four antennas should be equal. The phase-difference statistics are in radian units. As expected, the phase-difference variances increase with increasing antenna separation. The minimum and maximum observed phase differences during these data runs had changes as large as ±TT.

Figure 2 shows an intensity probability density function (PDF). Gaussian and lognormal PDFs having the same mean and variance are also plotted. There is little difference between the Gaussian and lognormal PDFs for such small values of variance. However, the data are clearly skewed and more nearly follow the lognormal PDF, as is expected theoretically, provided that the effects of absorption fluctuations are negligible. When absorption fluctua­ tions substantially influence the intensity variance, then the lognormal PDF is not observed.

Figure 3 shows the phase-difference PDF from antennas 2 and 3 of session 1, tape 24. A Gaussian PDF having the same mean and variance is also plotted. Clearly the phase difference is Gaussian, as is expected theoretically.

Figure 4 shows the structure function of phase versus receiver separation. The six receiver separations corre­ spond to the six antenna pairs. At a given receiver separation, the value of the structure function of phase is just the phase-difference variance for the corresponding antenna pair. Also plotted is a theoretical prediction for the 6:50 p.m. data using the rnicromet-value of Cn and assuming a 2.2-m otiter scale and a von Karman refractive-index spectrum. Using a 2.2-m outer scale produces a theoretical structure function of phase having nearly the same shape as the data.

Figure 5 shows the normalized intensity variance plotted versus the theoretical formula for a spherical wave propagating through inertial-range turbulence. Here, C2? is deduced from the micromet data. Data agreeing perfectly with theory would lie on the straight line. The slight (~ 12%) lack of agreement could be caused by the outer scale of turbulence and possibly by inaccurate calibration of the Lyman-a hygrometer.

Figure 6 contains a log-log plot of (f/f0 ) times the log-amplitude spectrum Wx versus normalized frequency (f/fo)- The spectrum Wx is normalized to the log-amplitude variance such that the area under the curve is unity. The frequency f0 - v/v2;rAL, where v is the cross-path component of windspeed, X is the wavelength, and L - 1.4 km is the millimeter-wave path length. The dotted (solid) fluctuating curve represents the low (high) frequency Fourier transform of 35 min of log-amplitude data taken at 142 GHz. The solid theory curve fits the data quite well until the high frequency tail beyond log (f/f0 ) = l» where aperture averaging effects are important. The dashed curve is a plot of the theory including aperture averaging effects; overall, the fit to the data is excellent. Deviations at low frequen­ cies above the "theory" curve are most likely due to receiver drift. It is possible from the theory to estimate the cross-path velocity from the location of the peak. The peak is predicted at log (f/f0 ) — 0.43. In the case shown, the cross-path velocity estimate from the millimeter wave scintillations agrees with the propellor-vane anemometer data.

Figure 7 shows a measured log-amplitude spectrum as a function of temporal frequency in Hz. The high-fre­ quency part above 0.5 Hz is similar to the result in Fig. 6; this part of the spectrum is dominated by refraction fluctuations and is amenable to traditional theory. The low-frequency part in Fig. 7 is caused by an absorption event during the run; specifically, the humidity increased along the entire path during the run. Although we have a theory applicable to absorption fluctuations of scale much smaller than the path length, the event resulting in the spectrum in Fig. 7 is not described by existing theory. Such an event produces an intensity PDF that is not lognormal. Obviously from Fig. 7, this absorption event produced most of the intensity variance, violating the assumptions that produce agreement in Figs. 5 and 6.

Figures 8 and 9 show theoretical curves superimposed over the phase-difference spectra from the data for antenna pair (1,2) separated by Q\ 2 - 1-43 m and antenna pair (1,4) separated by Q {4 = 10 m. We used the value L0 — 2.8 m and selected our curves to fit the data based on the ratios Q[2/L0 =0.51 and Q\*/L0 = 3.5 appropriate to each antenna pair. The resulting fit is quite good. We could also estimate crosswind from the peak of the spec­ trum if we knew the accurate L0 from other independent measurements.

ACKNOWLEDGMENT

The research was supported in part by the U.S. Army Research Office under Contracts DAAG29-8 l-K-0173, DAAG29-77-C-0026 and MIPR 122-85.

SPIE Vol. 1115 Propagation Engineering (1989) / 235

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Table 1. Millimeter -wave statistics obtained by averaging all oftapes 20 and 24 of session 1. July 1983.

Antenna Intensitynumber variance

Antenna Antenna Phase -pair spacing difference

(m) variance

Tape 20 Tape 24 Tape 20 Tape 24

1 0.0069 0.021 1&2 1.43 0.025 0.0812 0.0060 0.022 2&3 2.86 0.064 0.1933 0.0068 0.023 1&3 4.29 0.106 0.3154 0.0090 0.030 3&4 5.71 0.133 0.408

2&4 8.57 0.164 0.56310.00 0.195 0.7031&4

/ /// / .e. //i/ /

// // /i' / Mot.Tronsmittor /' / Sto.2Von ., /,' /

Fig. 1. The instrument positions at the experiment site. The dashed and dotted linedenotes mm -wave propagation path (1.374 km): the long-dashed lines, the opticalpropagation paths (670 m each); and the short- dashed lines, the optical rain gaugepaths (50 m each). Solid lines show the flow of micometeorological data to the dataacquisition system in the receiver trailer. Antennas are numbered 1 to 5 in thereceiver trailer.

236 / SPIE Vol 1115 Propagation Engineering (1989)

Table 1. Millimeter-wave statistics obtained by averaging all of tapes 20 and 24 of session I. July 1983.

Antennanumber

Intensityvariance

Antennapair

Antennaspacing(m)

Phase-differencevariance

Tape 20 Tape 24

0.0069 0.0210.0060 0.0220.0068 0.0230.0090 0.030

Tape 20 Tape 24

1&22&31&33442&41&4

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.71

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.408

.563

.703

Receiver roller

Prevailing Wind

Weighing Bucket Rain Gauges

Fig. I. The instrument positions at the experiment site. The dashed and doited line denotes mm-wave propagation path (1.374 km): the long-dashed lines, the optical propagation paths (670 m each); and the short-clashed lines, the optical rain gauge paths (50 m each). Solid lines show the flow of micometeorological data to the data acquisition system in the receiver trailer. Antennas are numbered 1 to 5 in the receiver trailer.

236 / SPIE Vol. 1115 Propagation Engineering (1989)

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/01/2013 Terms of Use: http://spiedl.org/terms

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238 / SPIE Vol. 1115 Propagation Engineering (1989)

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238 / SPIE Vol. 1115 Propagation Engineering (1989)

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4. REFERENCES

I. N.A. Armand, A.N. Lomakin, and V.A. Sarkisyants, "Some results of an experimental investigation of thespectral characteristics of the phase difference of a radio signal in the surface layer of the atmosphere," RadioEng. Electron. Phys. 18, 618 -620 (1973).

2. G.M. Babler, "Scintillation effects at 4 and 6 GHz on a line -of -sight microwave link," IEEE Trans. Ant. Prop.AP -19, 574 -575 (1971).

3. J.R. Blakey, R.S. Cole, A.D. Sarma, and L. Silva Mello, "Measurement of atmospheric millimetre -wave phasescintillations in an absorption region," Electronics Letters 21, 486 -487 (1985).

4. R.A. Bohlander, R.W. McMillan, V.T. Brady, G.F. Kirkman, M.J. Sinclair, J.W. Larsen, M.L. Blyler, R.P.Lilly, D.O. Gallentine, S.F. Clifford, J.T. Priestley. R.J. Hill, R.E. Cupp, N.L. Ahshire, R.B. Fritz, W.Cartwright, G.R. Ochs, R.J. Lataiatis, J.J. Wilson, and G.M. Walford, "Observations of amplitude and angle -of- arrival scintillation in millimeter wave propagation caused by turbulence in clear air near the ground," Proc.8th International Conference on Infrared and Millimeter Waves, Dec. 12 -17, 1983, Miami Beach, FL, TH6.4(1983).

5. S.F. Clifford, R.J. Hill, J.T. Priestley, B.A. Bohlander, and R.W. McMillan : The spectra of amplitude andphase difference fluctuations of millimeter waves propagating in clear air. Proc. URSI, July 18 - Aug. 1, 1986,Durham, NH (1986).

6. S.F. Clifford, R.J. Hill, R.B. Fritz, R.A. Bohlander, and R.W. McMillan, "Line -of -sight millimeter -wavepropagation characteristics, " Conference Preprint No. 419, AGARD, Scattering and Propagation in RandomMedia, 16 -1 - 16 -17, May 1987, Rome, Italy.

7. R.S. Cole, A.D. Sarma, and L. Silva Mello, "Measurement of atmospheric millimeter -wave phase scintilla-tions in an absorption region," Electronics Letters 21, 486 -487 (1985).

8. R.S. Cole. K.L. Ho. and N.D. Mavrokoukoulakis, "The effect of the outer scale of turbulence and wavelengthon scintillation fading at millimeter wavelengths," IEEE Trans. Ant. Prop. AP -26, 712 -715 (1978).

9. R.S. Cole, A.D. Sarma, and G.L. Siqueira, "Effect of meteorological conditions on scintillation fading in theoxygen absorption region," Appl. Opt. 27, 2261 -2265 (1988).

10. R.D. Etcheverry, G.R. Heidbreder, W.A. Johnson, and H.J. Wintrouh, "Measurements of spatial coherencein 3.2 mm horizontal transmission," IEEE Trans. Ant. Prop. AP -15, 136 -141 (1967).

11. J. Haddon, and E. Vilar, "Scattering induced microwave scintillations from clear air and rain on earth spacepaths and the influence of antenna aperture," IEEE Trans. Ant. Prop. AP -34, 646 -656 (1986).

12. C.G. Helmis, D.N. Asimakopoulas, C.A. Carouhalos, R.S. Cole, F.C. Medieros Filho, and D.A.R. Jayasuriya,"A quantitative comparison of the refractive index structure parameter determined from refractivity measure-ments and amplitude scintillation measurements at 36 GHz," IEEE Trans. Geoscience and Remote SensingGE -21, 221 -229 (1983).

13. M.H.A.J. Herben, and W. Koshiek, "A comparison of radiowave and in -situ observation of troposphericturbulence and wind velocity," Radio Science 19, 1057 -1068 (1984).

14. M.H.A.J. Herben, "Amplitude and phase scintillation measurements on 8.2 km line -of -sight path at 30GHz," Electronics Letters 18, 287 -289 (1982).

15. R.J. Hill, S.F.Clifford, J.T. Priestley, R.A. Bohlander, and R.W. McMillan, "Millimeter -wave scintillationclue to atmospheric surface -layer turbulence," Intl Conf. on Optical and Millimeter Wave Propagation andScattering in the Atmosphere. 259 -262, May 27 -30, 1986, Florence, Italy (1986).

16. R.J. Hill, R.A. Bohlander, S.F. Clifford. R.W. McMillan, J.T. Priestley, and W.P. Schoenfeld, "Turbulence -induced millimeter -wave scintillation compared with micrometeorological measurements," IEEE Trans. Geos-cience Remote Sensing 26, 330 -342 (1988).

17. R.J. Hill, J.T. Priestley, S.F. Clifford. W.P. Schoenfeld, R.W. McMillan, and R.A. Bohlander, "Instrumenta-tion. data validation and analysis, and results of the NOAA -GIT millimeter- wave propagation experiment,"Proc. of U.R.S.1., July 28 - Aug. 1, 1986, Durham, NH.

18. K.L. Ho, R.S. Cole, and N.D. Mavrokoukoulakis. "The effect of wind velocity on the amplitude scintillationsof millimeter radio waves," J. Atmos. Terr. Phys. 40, 443 -448 (1978).

SPIE Vol. 1115 Propagation Engineering (1989) / 239

4. REFERENCES

1. N.A. Armancl, A.N. Lomakin, and V.A. Sarkisyants, "Some results of an experimental investigation of the spectral characteristics of the phase difference ol a radio signal in the surface layer of the atmosphere," Radio Eng. Electron. Phys. 18, 618-620 (1973).

2. G.M. Babler, "Scintillation effects at 4 and 6 GHz on a line-of-sight microwave link," IEEE Trans. Ant. Prop. AP-19, 574-575 (1971).

3. J.R. Blakey, R.S. Cole, A.D. Sarma, and L. Silva Mello, "Measurement of atmospheric millimetre-wave phase scintillations in an absorption region," Electronics Letters 21, 486-487 (1985).

4. R.A. Bohlander, R.W. McMillan, V.T. Bracly, G.F. Kirkman, M.J. Sinclair, J.W. Larsen, M.L. Blyler, R.P. Lilly, p.O. Oallenline, S.F. Clifford, J.T. Priestley, R.J. Hill, R.E. Cupp, N.L. Abshire, R.B. Fritz, VV. Cartwright, G.R. Ochs, R.J. Lataiatis, J.J. Wilson, and G.M. Walford, "Observations of amplitude and angle- of-arrival scintillation in millimeter wave propagation caused by turbulence in clear air near the ground," Proc. 8th International Conference on Infrared and Millimeter Waves, Dec. 12-17, 1983, Miami Beach, FL, TH6.4 (1983).

5. S.F. Clifford, R.J. Hill, J.T. Priestley, B.A. Bohlander, and R.W. McMillan : The spectra of amplitude and phase difference fluctuations of millimeter waves propagating in clear air. Proc. URSl, July 18 - Aug. 1, 1986, Durham, NH (1986).

6. S.F. Clifford, R.J. Hill, R.B. Fritz, R.A. Bohlander, and R.W. McMillan, "Line-of-sight millimeter-wave propagation characteristics," Conference Preprint No. 419, AGARD, Scattering and Propagation in Random Media, 16-1 - 16-17, May 1987, Rome, Italy.

7. R.S. Cole, A.D. Sarma, and L. Silva Mello, "Measurement of atmospheric millimeter-wave phase scintilla­ tions in an absorption region," Electronics Letters 21, 486-487 (1985).

8. R.S. Cole, K.L. Ho, and N.D. Mavrokoukoulakis, "The effect of the outer scale of turbulence and wavelength on scintillation fading at millimeter wavelengths," IEEE Trans. Ant. Prop. AP-26, 712-715 (1978).

9. R.S. Cole, A.D. Sarma, and G.L. Siqueira, "Effect of meteorological conditions on scintillation fading in the oxygen absorption region," Appl. Opt. 27, 2261-2265 (1988).

10. R.D. Etcheverry, G.R. Heiclbreder, W.A. Johnson, and H.J. Wintroub, "Measurements of spatial coherence in 3.2 mm horizontal transmission," IEEE Trans. Ant. Prop. AP-15, 136-141 (1967).

11. J. Hadclon, and E. Vilar, "Scattering induced microwave scintillations from clear air and rain on earth space paths and the influence of antenna aperture," IEEE Trans. Ant. Prop. AP-34, 646-656 (1986).

12. C.G. Helrnis, D.N. Asimakopoulas, C.A. Caroubalos, R.S. Cole, F.C. Medieros Filho, and D.A.R. Jayasuriya, "A quantitative comparison of the refractive index structure parameter determined from refractivity measure­ ments and amplitude scintillation measurements at 36 GHz," IEEE Trans. Geoscience and Remote Sensing GE-21, 221-229 (1983).

13. M.H.A.J. Herben, and W. Koshiek, "A comparison of radiowave and in-situ observation of tropospheric turbulence and wind velocity," Radio Science 19, 1057-1068 (1984).

14. M.H.A.J. Herben, "Amplitude and phase scintillation measurements on 8.2 km line-of-sight path at 30 GHz," Electronics Letters 18, 287-289 (1982).

15. R.J. Hill, S.F.Clifford, J.T. Priestley, R.A. Bohlander, and R.W. McMillan, "Millimeter-wave scintillation clue to atmospheric surface-layer turbulence," Int'l Conf. on Optical and Millimeter Wave Propagation and Scattering in the Atmosphere. 259-262, May 27-30, 1986, Florence, Italy (1986).

16. R.J. Hill, R.A. Bohlander, S.F. Clifford. R.W. McMillan, J.T. Priestley, and W.P. Schoenfeld, "Turbulence- induced millimeter-wave scintillation compared with micrometeorological measurements," IEEE Trans. Geos­ cience Remote Sensing 26, 330-342 (1988).

17. R.J. Hill, J.T. Priestley, S.F. Clifford, W.P. Schoenfeld, R.W. McMillan, and R.A. Bohlander, "Instrumenta­ tion, data validation and analysis, and results of the NOAA-G1T millimeter- wave propagation experiment," Proc. of U.R.S.I., July 28 - Aug. I, 1986, Durham, NH.

18. K.L. Ho, R.S. Cole, and N.D. Mavrokoukoulakis. "The effect of wind velocity on the amplitude scintillations of millimeter radio waves," J. Atmos. Terr. Phys. 40, 443-448 (1978).

SPIE Vol. 1115 Propagation Engineering (1989) / 239

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/01/2013 Terms of Use: http://spiedl.org/terms

19. K.L. Ho, N.D. Mavrokoukoulakis, and R.S. Cole, "Determination of the atmospheric refractive index struc-ture parameters from refractivity measurements and amplitude scintillation measurements at 36 GHz," J. At-mos. Terr. Phys. 40, 745 -747 (1978).

20. K.L. Ho, R.S. Cole, and N.D. Mavrokoukoulakis, "Spectral analysis of anomalous millimeter -wave amplitudescintillations in a town environment," IEEE Trans. Ant. Prop. AP -28, 941 -942 (1980).

21. K.L. Ho, N.D. Mavrokoukoulakis, and R.S. Cole, "Wavelength dependence of scintillation fading at 110 and36 GHz," Electronics Letters 13, 181 -182 (1977).

22. K.L. Ho, N.D. Mavrokoukoulakis, and R.S. Cole, "Propagation studies on a line -of -sight microwave link at36 GHz and I LO GHz," Microwaves, Optics and Acoustics 3, 93 -98 (1979).

23. H.B. Janes and M.C. Thompson, Jr., "Comparison of observed and predicted phase -front distortion in line -of -sight microwave signals," IEEE Trans. Ant. Prop. AP -21, 263 -266 (1973).

24. H.B. Janes, M.C. Thompson, Jr., D. Smith, and A.W. Kirkpatrick, "Comparison of simultaneous line -of-sight signals at 9.6 and 34.5 GHz," IEEE Trans. Ant. Prop. AP -18, 447 -451 (1970).

25. I-1.B. Janes, M.C. Thompson, Jr., and D. Smith, "Tropospheric noise in microwave range- difference meas-urements," IEEE Trans. Ant. Prop. AP -21, 256 -260 (1973).

26. D.A.R. Jayasuriya, F.C. Medeiros Filho, and R.S. Cole, "Amplitude coherence in an absorption region,"IEEE Trans. Ant. Prop. AP -30, 1242 -1244 (1982).

27. D.A.R. Jayasuriya, F.C. Medeiros Filho, and R.S. Cole, "Scintillation fading in an absorption region," IEEEConference Publication no. 195, 221 -224 (1981).

28. M.B. Kanevskii, "The problem of the influence of absorption on amplitude fluctuations of submillimeter radiowaves in the atmosphere," Radiophysics and Quantum Electronics 15, 1486 -1487 (1972).

29. R.W. Lee, and A.T. Waterman, Jr., "Space correlations of 35 GHz transmissions over a 28 -km path," RadioScience 3, 135-139 (1968).

30. P.A. Mandics, R.W. Lee, and A.T. Waterman, Jr., "Spectra of short -term fluctuations of line -of -sight sig-nals: Electromagnetic and acoustic," Radio Science 8, 185 -201 (1973).

31. P.A. Mandics, J.C. Harp, R.W. Lee, and A.T. Waterman, Jr., "Multifrequency coherences of short -termfluctuations of line -of -sight signals -- Electromagnetic and acoustic," Radio Science 9, 723 -731 (1974).

32. N.D. Mavrokoukoulakis, K.L. Ho, and R.S. Cole, "Temporal spectra of atmospheric amplitude scintillation at110 GHz and 36 GHz," IEEE Trans. Ant. Prop. AP -26, 875 -877 (1978).

33. N.D. Mavrokoukoulakis, K.L. Ho, and R.S. Cole, "Amplitude scintillations in a town environment," Elec-tronics Letters 13, 391 -392 (1977).

34. R.W. McMillan, R.A. Bohlander, D.G. Bauerle, G.R. Ochs, R.J. Hill, S.F. Clifford, and J. Nemarich, "Milli-meter wave atmospheric turbulence measurements: Preliminary results," SPIE 337, 88 -95, May 6 -7, 1982,Arlington, VA (1982).

35. R.W. McMillan, R.A. Bohlander, R.H. Platt, D.M. Guillory, J.T. Priestley, R.J. Hill, S.F. Clifford. R.E.Cupp, and J. Wilson, "Atmospheric turbulence measurement system," SPIE Tech. Symp. East '85, April8 -12, 1985, Arlington, VA.

36. R.W. McMillan, R.A. Bohlander, G.R. Ochs, R..1. Hill, and S.F. Clifford, "Millimeter wave atmosphericturbulence measurements: Preliminary results and instrumentation for future measurements," Optical Engi-neering 22, 32 -39 (1983).

37. R.W. 1NIcMillan, R.A. Bohlander, E.M. Peterson, R.J. Hill, and S.F. Clifford, "Effects of turbulence andinclement weather on millimeter wave propagation," 1GARSS '87, May 18 -21, 1987, Ann Arbor, MI.

38. R.W. McMillan. R.A. Bohlander, and G.R. Ochs, "Instrumentation for millimeter wave turbulence measure-ments. Atmospheric Effects on Electro- Optical, Infrared, and Millimeter Wave on Systems Performance,"SPIE 305, 253 -260, Aug. 27 -28, 1981, San Diego, CA (1981).

39. R.W. McMillan, R.A. Bohlander, D.M. Guillory, R.H. Platt, J.M. Cotton, Jr., S.F. Clifford. J.T. Priestley,and R.J. Hill, "Millimeter wave atmospheric turbulence measurements," Proc. 9th Intl. Conf. on Infrared andMillimeter Waves 463 -464, Oct. 1984, Osaka (Takarazuka), Japan (1984).

240 / SPIE Vol. 1115 Propagation Engineering (1989)

19. K.L. Ho, N.D. Mavrokoukoulakis, and R.S. Cole, "Determination of the atmospheric refractive index struc­ ture parameters from refractivity measurements and amplitude scintillation measurements at 36 GHz," J. At- mos. Terr. Phys. 40, 745-747 (1978).

20. K.L. Ho, R.S. Cole, and N.D. Mavrokoukoulakis, "Spectral analysis of anomalous millimeter-wave amplitude scintillations in a town environment," IEEE Trans. Ant. Prop. AP-28, 941-942 (1980).

21. K.L. Ho, N.D. Mavrokoukoulakis, and R.S. Cole, "Wavelength dependence of scintillation fading at 110 and 36 GHz," Electronics Letters J3, 181-182 (1977).

22. K.L. Ho, N.D. Mavrokoukoulakis, and R.S. Cole, "Propagation studies on a line-of-sight microwave link at 36 GHz and 110 GHz," Microwaves, Optics and Acoustics 3, 93-98 (1979).

23. H.B. Janes and M.C. Thompson, Jr., "Comparison of observed and predicted phase-front distortion in line- of-sight microwave signals," IEEE Trans. Ant. Prop. AP-21, 263-266 (1973).

24. H.B. Janes, M.C. Thompson, Jr., D. Smith, and A.W. Kirkpatrick, "Comparison of simultaneous line-of- sight signals at 9.6 and 34.5 GHz," IEEE Trans. Ant. Prop. AP-18, 447-451 (1970).

25. H.B. Janes, M.C. Thompson, Jr., and D. Smith, "Tropospheric noise in microwave range-difference meas­ urements," IEEE Trans. Ant. Prop. AP-21, 256-260 (1973).

26. D.A.R. Jayasuriya, F.C. Medeiros Filho, and R.S. Cole, "Amplitude coherence in an absorption region," IEEE Trans. Ant. Prop. AP-30, 1242-1244 (1982).

27. D.A.R. Jayasuriya, F.C. Medeiros Filho, and R.S. Cole, "Scintillation fading in an absorption region," IEEE Conference Publication no. 195, 221-224 (1981).

28. M.B. Kanevskii, "The problem of the influence of absorption on amplitude fluctuations of submillimeter radio waves in the atmosphere," Radiophysics and Quantum Electronics 15, 1486-1487 (1972).

29. R.W. Lee, and A.T. Waterman, Jr., "Space correlations of 35 GHz transmissions over a 28-km path," Radio Science 3, 135-139 (1968).

30. P.A. Mandics, R.W. Lee, and A.T. Waterman, Jr., "Spectra of short-term fluctuations of line-of-sight sig­ nals: Electromagnetic and acoustic," Radio Science 8, 185-201 (1973).

31. P.A. Mandics, J.C. Harp, R.W. Lee, and A.T. Waterman, Jr., "Multifrequency coherences of short-term fluctuations of line-of-sight signals—Electromagnetic and acoustic," Radio Science 9, 723-731 (1974).

32. N.D. Mavrokoukoulakis, K.L. Ho, and R.S. Cole, "Temporal spectra of atmospheric amplitude scintillation at 110 GHz and 36 GHz," IEEE Trans. Ant. Prop. AP-26, 875-877 (1978).

33. N.D. Mavrokoukoulakis, K.L. Ho, and R.S. Cole, "Amplitude scintillations in a town environment," Elec­ tronics Letters 13, 391-392 (1977).

34. R.W. McMillan, R.A. Bohlander, D.G. Bauerle, G.R. Ochs, R.J. Hill, S.F. Clifford, and J. Nemarich, "Milli­ meter wave atmospheric turbulence measurements: Preliminary results," SPIE 337, 88-95, May 6-7, 1982, Arlington, VA (1982).

35. R.W. McMillan, R.A. Bohlancler, R.H. Platt, D.M. Guillory, J.T. Priestley, R.J. Hill, S.F. Clifford, R.E. Cupp, and J. Wilson, "Atmospheric turbulence measurement system," SPIE Tech. Symp. East '85, April 8-12, 1985, Arlington, VA.

36. R.W. McMillan, R.A. Bohlancler, G.R. Ochs, R.J. Hill, and S.F. Clifford, "Millimeter wave atmospheric turbulence measurements: Preliminary results and instrumentation lor future measurements," Optical Engi­ neering 22, 32-39 (1983).

37. R.W. McMillan, R.A. Bohlander, E.M. Peterson, R.J. Hill, and S.F. Clifford, "Effects of turbulence and inclement weather on millimeter wave propagation," IGARSS '87, May 18-21, 1987, Ann Arbor, MI.

38. R.W. McMillan, R.A. Bohlander, and G.R. Ochs, "Instrumentation for millimeter wave turbulence measure­ ments. Atmospheric Effects on Electro-Optical, Infrared, and Millimeter Wave on Systems Performance," SPIE 305, 253-260, Aug. 27-28, 1981, San Diego, CA (1981).

39. R.W. McMillan, R.A. Bohlancler, D.M. Guillory, R.H. Platt, J.M. Cotton, Jr., S.F. Clifford, J.T. Priestley, and R.J. Hill, "Millimeter wave atmospheric turbulence measurements," Proc. 9th Intl. Conl. on Infrared and Millimeter Waves 463-464, Oct. 1984, Osaka (Takarazuka), Japan (1984).

240 / SPIE Vol. 1115 Propagation Engineering (1989)

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/01/2013 Terms of Use: http://spiedl.org/terms

40. F.C. Medeiros Filho, D.A.R. Jayasuriya, R.S. Cole, and C.G. Helmis, "Spectral density of millimeter -waveamplitude scintillation in an absorption region," IEEE Trans. Ant. Prop. AP -31, 672 -676 (1983).

41. F.C. N'lecleiros Filho, D.A.R. Jayasuriya, and R.S. Cole, "Tropospheric effects on line -of -sight links at 36GHz and 55 GHz," Proc. IEEE 130, 679 -687 (1983).

42. F.C. Medeiros Filho, D.A.R. Jayasuriya, and R.S. Cole, "Spectral density of amplitude scintillations on a 55GHz line -of -sight link," Electronics Letters 17, 25 -26 (1981).

43. F.C. Medeiros Filho, D.A.R. Jayasuriya. and R.S. Cole, "Spectral density of millimetre wave amplitude scintil-lations in an absorption region," IEEE Trans. Ant. Prop. AP -31, 672 -676 (1983).

44. F.C. i\Iecleiros Filho, D.A.R. Jayasuriya, and R.S. Cole, "Probability distribution of amplitude scintillations ona line -of -sight link at 36 GHz and 55 GHz," Electronics Letters 17, 393 -394 (1981).

45. N. Sengupta, M.K. Das Gupta, B.M. Reddy, H.N. Dutta, and S.K. Sarkar, "A comparative study of scintilla-tion analysis over two line -of -sight paths at 6.7 GHz and 7.6 GHz," IEEE Trans. Ant. Prop. AP -3I (1983).

46. M.C. Thompson, H.B. Janes. L.E. Wood, and D. Smith, "Phase and amplitude scintillations at 9.6 GHz onan elevated path," IEEE Trans. Ant. Prop. AP -23, 850 -584 (1975).

47. M.C. Thompson, L.E. Wood, H.B. Janes, and D. Smith, "Phase and amplitude scintillations in the 10 to 40GHz band," IEEE Trans. Ant. Prop. AP -23, 792 -797 (1975).

48. W.J. Vogel, .I.H. Davis, and C.E. Mayer, "Line-of-sight observations at 86 GHz with a very large and smallantenna," IEEE Trans. Ant. Prop. AP -32, 113 -118 (1984).

49. G.A. Anclreyev, and L.F. Chernaya, "Fluctuations in millimeter -wave beams propagating in a turbulent ab-sorbing troposphere. Telecom. Radio Eng. 33, 64 -74 (1978).

50. N.A. Armand, A.O. Izyumov, B.S. Polevoy, A.V. Sokolov, and Al. Topkov, "Fluctuation of millimeterracliowaves propagated through a turbulent atmosphere near the oxygen absorption line centered at the wave-length of 5 mm," Radio Eng. Elec. Physics 18, 492 -496 (1973).

51. N.A. Armand, A.O. Izyumov, and A.V. Sokolov, "Fluctuations of submillimeter waves in a turbulent atmos-phere," Radio Eng. Elec. Phys. 1.6, 1257 -1266 (1971).

52. P.C. Claspy and F.L. Merat, "Atmospheric propagation studies at near -millimeter wavelengths," SPIE 337,81 -86 (1982).

53. S.F. Clifford, "Temporal frequency spectra for a spherical wave propagating through atmospheric turbulence,"J. Opt. Soc. Am. 61, 1285 -1292 (1971).

54. S.F. Clifford and J.W. Strohbehn, "The theory of microwave line -of -sight propagation through a turbulentatmosphere," IEEE Trans. Ant. Prop. AP -18, 264 -274 (1970).

55. S.F. Clifford, and R.J. Lataitis, "Mutual coherence function for line -of -sight microwave propagation throughatmospheric turbulence," Radio Sci. 20, 221 -227 (1985).

56. A.S. Gurvich, "Effect of absorption on the fluctuation in signal level during atmospheric propagation," RadioEng. Elec. Phys. 13, 1687 -1694 (1968).

57. R.J. Hill, S.F. Clifford, and R.S. Lawrence, "Computed refraction and absorption fluctuations caused bytemperature, humidity, and pressure fluctuations --radio waves to 5 µm," NOAA Tech. Memo. ERL/WPL -59, June 1980.

58. R.J. Hill, S.F. Clifford, and R.S. Lawrence, "Refractive -index and absorption fluctuations in the infraredcaused by temperature, humidity, and pressure fluctuations," J. Opt. Soc. Am. 70, 1192 -1205 (1980).

59. R.J. Hill, and S.F. Clifford, "Contribution of water vapor monomer resonances to fluctuations of refractionand absorption for submillimeter through centimeter wavelength," Radio Science 16, 77 -82 (198 I).

60. A. Ishimaru, "Temporal frequency spectra of multifrequency waves in turbulent atmosphere," IEEE Trans.Ant. Prop. AP -20, 10 -19 (1972).

61. A.O. lzyumov, "Amplitude and phase fluctuation of a plane monochromatic submillimeter wave in a near -ground layer of moisture -containing air," Radio Eng. Elec. Physics 13, 1009 -1013 (1968).

SPIE Vol. 1115 Propagation Engineering (1989) / 241

40. F.C. Medeiros Filho, D.A.R. Jayasuriya, R.S. Cole, and C.G. Helmis, "Spectral density of millimeter-wave amplitude scintillation in an absorption region," IEEE Trans. Ant. Prop. AP-31, 672-676 (1983).

41. F.C. Medeiros Filho, D.A.R. Jayasuriya, and R.S. Cole, "Tropospheric effects on line-of-sight links at 36 GHz and 55 GHz," Proc. IEEE 130, 679-687 (1983).

42. F.C. Medeiros Filho, D.A.R. Jayasuriya, and R.S. Cole, "Spectral density of amplitude scintillations on a 55 GHz line-of-sight link," Electronics Letters 17, 25-26 (1981).

43. F.C. Medeiros Filho, D.A.R. Jayasuriya. and R.S. Cole, "Spectral density of millimetre wave amplitude scintil­ lations in an absorption region," IEEE Trans. Ant. Prop. AP-31, 672-676 (1983).

44. F.C. Medeiros Filho, D.A.R. Jayasuriya, and R.S. Cole, "Probability distribution of amplitude scintillations on a line-of-sight link at 36 GHz and 55 GHz," Electronics Letters 17, 393-394 (1981).

45. N. Sengupta, M.K. Das Gupta, B.M. Reddy, H.N. Dulla, and S.K. Sarkar, "A comparative study of scintilla­ tion analysis over two line-of-sight paths at 6.7 GHz and 7.6 GHz," IEEE Trans. Ant. Prop. AP-31 (1983).

46. M.C. Thompson, H.B. Janes, L.E. Wood, and D. Smith, "Phase and amplitude scintillations at 9.6 GHz on an elevated path," IEEE Trans. Ant. Prop. AP-23, 850-584 (1975).

47. M.C. Thompson, L.E. Wood, H.B. Janes, and D. Smith, "Phase and amplitude scintillations in the 10 to 40 GHz band," IEEE Trans. Ant. Prop. AP-23, 792-797 (1975).

48. W.J. Vogel, J.H. Davis, and C.E. Mayer, "Line-of-sight observations at 86 GHz with a very large and small antenna," IEEE Trans. Ant. Prop. AP-32, 113-118 (1984).

49. G.A. Andreyev, and L.F. Chernaya, "Fluctuations in millimeter-wave beams propagating in a turbulent ab­ sorbing troposphere. Telecom. Radio Eng. 33, 64-74 (1978).

50. N.A. Armand, A.O. Izyumov, B.S. Polevoy, A.V. Sokolov, and A.I. Topkov, "Fluctuation of millimeter radiowaves propagated through a turbulent atmosphere near the oxygen absorption line centered at the wave­ length of 5 mm," Radio Eng. Elec. Physics 18, 492-496 (1973).

51. N.A. Armand, A.O. Izyumov, and A.V. Sokolov, "Fluctuations of submillimeter waves in a turbulent atmos­ phere," Radio Eng. Elec. Phys. 16, 1257-1266 (1971).

52. P.C. Claspy and F.L. Merat, "Atmospheric propagation studies at near-millimeter wavelengths," SP1E 337, 81-86 (1982).

53. S.F. Clifford, "Temporal frequency spectra for a spherical wave propagating through atmospheric turbulence," J. Opt. Soc. Am. 61, 1285-1292 (1971).

54. S.F. Clifford and J.W. Strohbehn, "The theory of microwave line-of-sight propagation through a turbulent atmosphere," IEEE Trans. Ant. Prop. AP-18, 264-274 (1970).

55. S.F. Clifford, and R.J. Lataitis, "Mutual coherence function for line-of-sight microwave propagation through atmospheric turbulence," Radio Sci. 20, 221-227 (1985).

56. A.S. Gurvich, "Effect of absorption on the fluctuation in signal level during atmospheric propagation," Radio Eng. Elec. Phys. 13, 1687-1694 (1968).

57. R.J. Hill, S.F. Clifford, and R.S. Lawrence, "Computed refraction and absorption fluctuations caused by temperature, humidity, and pressure fluctuations—radio waves to 5 juim," NOAA Tech. Memo. ERL/ WPL-59, June 1980.

58. R.J. Hill, S.F. Clifford, and R.S. Lawrence, "Refractive-index and absorption fluctuations in the infrared caused by temperature, humidity, and pressure fluctuations," J. Opt. Soc. Am. 70, 1192-1205 (1980).

59. R.J. Hill, and S.F. Clifford, "Contribution of water vapor monomer resonances to fluctuations of refraction and absorption for submillimeter through centimeter wavelength," Radio Science 16, 77-82 (1981).

60. A. Ishimaru, "Temporal frequency spectra of multifrequency waves in turbulent atmosphere," IEEE Trans. Ant. Prop. AP-20, 10-19 (1972).

61. A.O. Izyumov, "Amplitude and phase fluctuation of a plane monochromatic submillimeter wave in a near- ground layer of moisture-containing air," Radio Eng. Elec. Physics 13, 1009-1013 (1968).

SPIE Vol. 1115 Propagation Engineering (1989) / 241

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62. R.W. Lee and J.C. Harp, "Weak scattering in random media, with applications to remote probing," Proc.IEEE 57, 375 -406 (1969).

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65. R.M. Manning, F.L. Merat, and P.C. Claspy, "Theoretical investigation of millimeter wave propagationthrough a clear atmosphere -I," SPIE 337, 67 -80, 1982.

66. R.W. McMillan, J.C. Wiltse, and D.E. Snider, "Atmospheric turbulence effects on millimeter wave propaga-tion," IEEE Electronics and Aerospace Systems Conference, 129 -134, 1979.

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68. R.H. Ott, "Temporal radio frequency spectra of multifrequency waves in a turbulent atmospherecharacaterized by a complex refractive index," IEEE Trans. Ant. Propagat. AP -25, 254 -260 (1977).

69. R.II. Ott, and M.C. Thompson, Jr., "Atmospheric amplitude spectra in an absorption region," IEEE Trans.Ant. Prop. AP -26, 329 -332 (1978).

70. R.H. Ott, "Bandwidth limitations in EM transmissions imposed by clear air turbulence," 1CC ConferenceRecord, IEEE Catalog No. 75CH0971- 2CSCB, 1, 15 -6 - 15 -9, 1975.

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73. R.J. Hill, W.P. Schoenfeld, J.P. Riley, J.T. Priestley, S.F. Clifford, S.P. Eckes, R.A. Bohlander, and R.W.McMillan. "Data analysis of the NOAA /GIT millimeter wave propagation experiment near Flatville, Illinois,"NOAA Tech. Rep., ERL 429 -WPL60 (1985).

74. R.A. Bohlander, R.W. McMillan, E.M. Patterson, S.F. Clifford, R.J. Hill, J.T. Priestley, and W.P. Schoen-feld, "Fluctuations in millimeter -wave signals propagated through inclement weather," IEEE Trans. Geosci.Remote Sens. 26, 343 -354 (1988).

75. R.A. Bohlander, R.W. Mcl\lillan, D.M. Guillory, R.H. Platt, S.F. Clifford, J.T. Priestley, R.J. Hill, R. Olsen,and B. Rischel, "Millimeter wave transmission fluctuations due to snow," Proc. of the SNOW Symposium IV,Aug. 1984, Hanover, NH (1984).

76. R.A. Bohlander. R.W. McMillan, D.M. Guillory, R.J. Hill, J.T. Priestley, S.F. Clifford, and R. Olsen, "Fluc-tuations in millimeter -wave signals," Conference Digest of the 10th Int. Conf. on Infrared and MillimeterWaves, December 9 -13, 1985, Lake Buena Vista, FL (1985).

242 / SPIE Vol 1115 Propagation Engineering (1989)

62. R.W. Lee and J.C. Harp, "Weak scattering in random media, with applications to remote probing," Proc. IEEE 57, 375-406 (1969).

63. R.W. Lee, "Aperture effects on the spectrum of amplitude scintillation," Radio Science 6, 1059-1060 (1971).

64. H.J. Liebe, "An updated model for millimeter-wave propagation in moist air," Radio Science 20, 1069-1089 (1985).

65. R.M. Manning, F.L. Merat, and P.C. Claspy, "Theoretical investigation of millimeter wave propagation through a clear atmosphere-1," SPIE 337, 67-80, 1982.

66. R.W. McMillan, J.C. Wiltse, and D.E. Snider, "Atmospheric turbulence effects on millimeter wave propaga­ tion," IEEE Electronics and Aerospace Systems Conference, 129-134, 1979.

67. R.M. Ott, and M.C. Thompson, Jr., "Characteristics of a radio link in the 55 to 65 GHz range," IEEE J. Ant. Prop. AP-24, 873-877 (1976).

68. R.H. Ott, "Temporal radio frequency spectra of multifrequency waves in a turbulent atmosphere characaterized by a complex refractive index," IEEE Trans. Ant. Propagat. AP-25, 254-260 (1977).

69. R.H. Ott, and M.C. Thompson, Jr., "Atmospheric amplitude spectra in an absorption region," IEEE Trans. Ant. Prop. AP-26, 329-332 (1978).

70. R.H. Ott, "Bandwidth limitations in EM transmissions imposed by clear air turbulence," ICC Conference Record, IEEE Catalog No. 75CH0971-2CSCB, 1, 15-6 - 15-9, 1975.

71. V.I. Tatarski, The Effect of the Turbulent Atmosphere on Wave Propagation. Springfield, PA: National Tech­ nical Information Service, U.S. Department of Commerce, 1971.

72. A.D. Wheelon, "Relation of radio measurements to the spectrum of tropospheric dielectric fluctuations," J. Appl. Physics 28, 684-693 (1957).

73. R.J. Hill, W.P. Schoenfeld, J.P. Riley, J.-T. Priestley, S.F. Clifford, S.P. Eckes, R.A. Bohlancler, and R.W. McMillan, "Data analysis of the NOAA/GJT millimeter wave propagation experiment near Flatville, Illinois," NOAA Tech. Rep., ERL 429-WPL60 (1985).

74. R.A. Bohlander, R.W. McMillan, E.M. Patterson, S.F. Clifford, R.J. Hill, J.T. Priestley, and W.P. Schoen­ feld, "Fluctuations in millimeter-wave signals propagated througli inclement weather," IEEE Trans. Geosci. Remote Sens. 26, 343-354 (1988).

75. R.A. Bohlander, R.W. McMillan, D.M. Guillory, R.H.Plait, S.F. Clifford, J.T. Priestley, R.J. Hill, R. Olsen, and B. Rischel, "Millimeter wave transmission fluctuations due to snow," Proc. of the SNOW Symposium IV, Aug. 1984, Hanover, NH (1984).

76. R.A. Bohlander, R.W. McMillan, D.M. Guillory, R.J. Hill, J.T. Priestley, S.F. Clifford, and R. Olsen, "Fluc­ tuations in millimeter-wave signals," Conference Digest of the 10th Int. Conf. on Infrared and Millimeter Waves, December 9-13, 1985, Lake Buena Vista, FL (1985).

242 / SPIE Vol. 1115 Propagation Engineering (1989)

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