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AUTHORITY31 Dec 1984, per document marking; NRLCode/5309 memo dtd 20 Feb 1997

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Copy No.2 3ESD-TR-73-270, Vol. II, Pt E -'

o SECRET

. ~AN/FPS-95 RESEARCH AND DEVELOPMENT PROGRAM(FINAL TECHNICAL REPORT, NAVAL RESEARCHLABORATORY, NOISE/INTERFERENCE ENVIRONMENT) (U) 60

J. F. ThomasonNaval Research Laboratory

_ Washington, D. C. 20375 D D C

March 1974 j- R' OLT 15 1975

Distribution limited to U.S. Gov't agencies only;Foreign Information; I February 1974. Other requestsforethis document must be referred to Hq AFSC (SDE).

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P12 ,•. -~ ~Declassify on: 31 December 1984,/

~ ~~sEARCH

Prepared for .... ."

DEPUTY FOR SURVEILLANCE AND CONTROL SYSTEMS Doc CONTROLHQ ELECTRONIC SYSTEMS DIVISION (AFSC)NoS ,44L. G. Hanscom Field, Bedford, MA 01730

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LEGAL NOTICE

When U. S. Government drawings, specifications or other data are used for anypurpose other than a definitely related government procurement operation, thegovernment thereby incurs no responsibility nor any obligation whatsoever; andthe fact that the government may have formulated, furnished, or in any way sup-plied the said drawings, specifications, or other data is not to be regarded byimplication or otherwise as in any manner licensing the holder or any other personor conveying any rights or permission to manufacture, use, or sell any patentedinvention that may in any way be related thereto.

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JAMES M. HEADRICK, Branch Head RICHARD W. CORAINE, Lt Col, USAF"Radar Techniques Branch Chief, 441 ARadar CDivision, Naval Research Laboratory Engineering Division

, .FO HECOMMAN

-DONALD . RECHT, Colonel, USAFSystem Program Director

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Ov~r-the-horizon radarRaar noise

Met or reflections

2.ABS gCT (Continue on reverse oide It necessary and Identify by block n'mbsr) (SECRET)Ii$ The operational performance of the AN/FPS-95 was degraded by theappearance of an enhanced noise which occurred in conjunction with the back-scatter. The present.'paper describes the experimental attempt to identifyPthat component of the noise which could arise from tnear range phenomena. For23 MHz, the cause -Is due primarily to line-of-sight meteor trail reflections,while for lower-operating frequencies there are indications of spreading ofsu-' :, wave clutter by antenna vibration.

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TABLE OF CONTENTS

Page

Abstract iv

I. INTRODUCTION I

lI_ II. TRANSMIT/RECEIVE SWITCH DEIONIZATION 1.

III. TRANSMITTER-INDUCED CORONA 1

IV. ANTENNA VIBRATION 2

V. METEORS 2

A. Identification of Near-Range Noise Sources 3B. Spectral Characteristics of Meteor Returns 4C. A Multiplicative Noise Burst 5D. Antenna Elevation Patterns Derived from Meteor Data 5E. Determination of Scattering Coefficient for the Meteor Flux 7

VI. CONCLUSIONS 8SiVII. RECOMMENDATIONS FOR FUTURE WORK 9

i VIII. ACKNOWLEDGMENTS 9

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ABSTRACT(Secret)

The operational performance of the AN/FPS-95 was degraded by theappearance of an enhanced noise which occurred in conjunction with thebackscatter. The present paper describes the experimental attempt toidentify that component of the noise which could arise from near rangephenomena. For 23 MHz, the cause is due primarily to line-of-sight meteortrail reflections, while for lower operating frequencies there are indica-

iI tions of spreading of surface wave clutter by antenna vibration.

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This report represents work performed by the Naval Research Laboratory(NRL) to carry out for the U. S. Air Force the investigation of certainOver-the-Horizon (OTH) techniques using the AN/FPS-95 Radar. This Researchand Development (R&D) work was conducted by NRL in direct technical supportto the Over-the-Horizon Program Office (OCS) of the Electronic SystemsDivision (AFSC).

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FINAL TECHNICAL REPORT ON THE AN/FPS-95 RESEARCH AND DEVELOPMENT PROGRAM[ •Vol. II, Part E. NOISE/INTERFERENCE ENVIRONMENT (U)

I. INTRODUCTION (U)

(S) During the course of its first year's operation the performanceU- of the AN/FPS-95 was degraded by the occurrence of an enhanced noise which

appeared in conjunction with the backscatter. To determine the causes ofthis "clutter-related noise" the ESD Scientific Assessment Committee wasestablished in January 1973. A test plan was developed consisting of sevenspecific experiments. The present paper is a report on the experiment toidentify the source of that component of the excess noise that could occurin the near range.

(S) The mechanisms postulated by the Scientific Assessment Committeefor the production of the short-range noise were transmit/receive switchdeionization, transmitter-induced corona, antenna vibration, and meteors.That portion of the noise appearing in the skip zone just short of theclutter is thought to be clutter related and is excluded from considerationfor this test.

II. TRANSMIT/RECEIVE SWITCH DEIONIZATION (U)

(S) Extensive tests were performed on the receiver and the transmit/receive switch during the Category II tests and DVST. These tests show thatthe solid state duplexer has no measurable effect after 24 microseconds fromits turnoff time. However, these tests also show a set of transients asso-ciated with gating the receiver off during the transmit pulse period. Thisgate has a rise time on the order of 100 nanoseconds and gates any signalpresent in the receiver preselector passband. Sidebands generated by gatingsignals in the preselector passband appear in the receiver passband. Becausethe time constant associated with these sidebands is that of the crystalfilter in the receiver, only the first and last range samples are contaminated.However, the postdetection filter in the on-line signal processor has a muchlonger time constant and smears the transient over several range cells if thetransient is allowed to reach the processor. During the DVST period thereceiver gating was modified to limit receiver off-time to the -transmissioninterval. Gating of data to the signal processor was provided by restrictingthe range samples sent to the digital-to-analog converter. This modification 3Nalleviated the on-line near-range noise problem somewhat. As will be seenfrom data presented later in this report, for off-line signal processing,where range samples are treated independently, the transient contaminatesonly the first range cell.

III. TRANSMITTER-INDUCED CORONA (U)

(S) Corona detection tests were run on 13 March 1973 between 0800Z andI 0930Z. The detection equipment used was a Singer NM-25T, radio interference

field intensity measuring equipment. The NM-25T was mounted on the platformoutside of door 8. Door 8 is in the antenna backlobe in line with string 4.While operating the radar at full power the NM-25T was used to scan the fre- f•quency range from 150 kHz to 30 MHz for signals produced by antenna corona. "a

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Although the low frequency part of the spectrum was thought tc be the mostsensitive indicator of the presence of antenna corona, no signals relatedto the AN/FPS-95 operation could be found in this part of the spectrum.However, with the system operating on 6.97 MHz evidence of antenna coronawas found by listening to the fourth harmonic at 27.9 MHz. The level ofthis harmonic was greatly influenced by the power level of transmitteroperation and by the particular antenna string in use. This is apparentlythe antenna corona or arcing which produces harmonics up into the televisionbroadcast band and has caused television interference in the vicinity •;.operating below 10.5 MHz. This corona has been the subject of an inter;.:investigation as the result of its link with the television interference.Numerous photographs and measurements have been maer by the investigators.Although the television interference investigation had establiohed a cutofffrequency of about 10.5 MHz for the effect of antenna arcing on televisionreception, attempts were made to detect evidence of corona when operatingabove 10.5 MHz. When operating on 15 MHz and scanning from 150 kHz to thesecond harmonic, no evidence of antenna corona could be found. Therefore,testing at 23 MHz for the antenna vibration and meteor hypothesis continuedwithout the installation of a corona monitor. There appears to be nothing tomonitor.

IV. ANTENNA VIBRATION (U)

(S) Several attempts were made to obtain a sufficient surface-wave-clutter-to-background-noise ratio to see clutter-related noise. Typically,30 or 40 dB clutter-to-noise ratio was achieved by operating at a low fre-quency on vertical polarization. For example, on 7.71 MHz with a 250-.jspulse the surface wave clutter was -40 dBm at 80 nmi. Background noise forthis data at 40 PRF and 10 seconds integration time was about -74 dBm. Datataken in this frequency range show an interesting fluctuation in the noisewhich appears to be associated with the surface wave clutter. The tests areinconclusive because of the possible contamination of the first range cellby gating transient already discussed.

(S) Figure 2 which is described in detail later shows data taken at23 MHz on 80 PRF which contains a -69 dBm surface wave clutter signal at 40nmi. Although the background noise for this data was down tn about -130 dBm,there was no evidence of spectral spreading of the surface wave clutter.No surface wave clutter was observable on the system antenna when operatingthe antenna horizontally polarized or when operating on the Yagi.

V. METEORS (U)

(U) Meteoric particles impinging on the atmosphere produce ionizationtrails at 80-to 110-km altitude which result in radar echoes in the near

range. Because of the large numbers of these echoes and their spread spec-trum natu, they are noise-like in character. The earth intercepts agproxi-

S~mately 10z meteoric particles per day ranging in mass from 10-8 to 10• grams i:

which produce electron line densities above 1010 electrons per meter. The

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product of the number of meteors of a given mass or greater and that masshas been found to be rougily constant at 105 grams. Since the electron linedensity produced by a specific meteoric particle is directly proportional to"that particle's mass, a similar relationship holds between the meteor rateand the electron density. Equation I gives the relationship between Ne, thenumtz of meteors per day producing a line electron density of De electrons[ " per meter or greater and the electron density De

DN = 1022 (1)

(U) Meteoric particles produce electron densities from about 1010electrons per meter upwards. Assuming the system can detect meteor trails

$from this density upwards, the rate of occurrence Re may be calculated•'- • 1 22

1 0 L ArRe Ar (2)DeAe

where Ar is the area in one resolution cell and Ae is the area of the earth.Evaluating the equation in dB for an electron density of 1010 electrons permeter, De = 100 dB, Ae = 147 dBsm, and Ar = 93 dBsm. This resolution cellrepresents one 20-nmi range cell at 280 nmi with an antenna beamwidth of 60.The resulting rate Re is 66 dB or 106.6 meteors per day. This may be reducedto a more meaningful rate of 101.6 meteors per second for a typical resolutioncell. Since the radar reflections are produced in a rather narrow altitudeband, the elevation angle antenna pattern is reflected in the amplitude-

j, range distribution of radar returns from this meteor flux.Ii

A. Identification of Near-Range Noise Sources (U)

(S) To test the meteor hypothesis a series of tests were performed in

which the operating frequency was held constant at about 23 MHz and, byvarying the time of day, data were taken both above and below the maximumusable frequency. Figure 1 shows one set of data taken above the groundbackscatter MUF using the Stanford Research Institute Facsimile processor.Data are displayed in the form of range-time-intensity plots. The MDS forthis setup is -115 dBm. The reduction in the range at which the near-rangenoise appears when switching from vertical o horizontal antenna polarizationis apparent and is consistent with the meteor hypothesis. This shift in

-' range is the result of the higher elevation pattern of the hdrizontallypolarized system antenaa as compared to the vertically polarized systemantenna. The transmitters were turned off between each run to confirm that

the noise being seen was in fact a radar return. In a paper which appeared -in the IRE Proceedings in October of 1955, 0. G. Villard et al publishedplots of the expedted and observed meteor activity as a function of azimuth

from a radar at Stanford University. These plots were for a radar locatedat 37.50 north latitude in the month of June and show a higher intensity ofmeteors toward the north. Figure 1 also shows a similar higher density inBeam 1 which Is the more northerly beam. A close examination of Figure 1

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shows a -100 dBm track beginning at about 0606Z and continuing until 0610Zwhen the transmitters were shut down. The radar range is about 100 nmi.Observation of the on-line system doppler-versus-range displays during thisperiod showed a strong line-of-sight aircraft target at 100 nmi. Thus, thisand other weaker tracks are attributed to line-of-sight aircraft. Theseweaker tracks are removed for the purpose of the meteor analysis by the useof median signal analysis. This analysis is described in later sections.

(S) In addition to the general shortening of the range to the maximumnoise density a close examination of the data for beam I - vertical shows anull at 275 nmi. If a meteor belt altitude of 95 km is assumed this rangecorresponds to an elevation angle of 8.50. Measurements made by Mr. CarmenMalagisi in August 1971 indicate a null in beam 1 - vertical elevationantenna p•.t,•rn at 9.50. Because of difficulties in integrating over a longperiod of tide wit.h the facsimile display and taking measurements of signallevels off of it, a more detailed analysis requires a different signal pro-cessing and display scheme. This analysis is described in the next section.

B. Spectral Characteristics of Meteor Returns (U)

(S) Figures 2, 3 and 4 are plots of doppler-range-power, with powerin each doppler-range cell being shown by a single character. A blank indi-cates that the power in that particular doppler-range cell was below the-135 dBm threshold chosen for these plots. The number zero indicates a-power above the threshold but not more than 3 dB above. The other numbersand the letters are used similarly in steps of 3 dB. Doppler frequency isshown along the bottom of the plot with zero at each edge. The entire dopplerextent is being displayed. Range runs from 40 nmi in steps of 20 nmi. Thesefigures are composites, each composed of 120 separate 3.2-second integrationtimes combined by averaging power over time in the frequency domain. Since

the pulse length for this data was 250 ps, no sample averaging was used.During the period when the data for these figureswere taken the operatingfrequency was 23 MHz which was above the maximum usable frequency.

(S) Operation above the maximum usable frequency allowed use of apulse repetition frequency of 8C Hz without the possibility of contaminationof the near-range noise data from long-range clutter and noise sources beingtime folded into the near range. This PRF allows a higher maximum unambiguousdoppler frequency than is practical to use below the MUF, thus more accurately $

characterizing the frequency components in the returns. The actual PRF usedfor this series of figures, 80 Hz, gives a maximum unambiguous doppler of±40 Hz. An examination of the figures shows that most of the energy from themeteor activity is concentrated within ±20 Hz of zero frequency. These fig- Lures also confirm the shift in amplitude versus range characteristic whenantenna elevation patterns are changed. In a later section, it is shown thatthe echoes in these illustrations approximately match those expected based M

on the assumed meteor flux and antenna patterns, Deviations are attributed

to imperfections in the antenna patterns. jui

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C. A Multipl.cative Noise Burst (U)

(S) In order to take data below the maximum usable frequency a verylow pulse repetition frequency is required to unfold all of the clutter andnoise sources thus insuring that the near-range noise data are not contam-inated by time-folded returns. The data shown in Figures 5, 6 and 7 weretaken with a pulse repetition frequency of 10 Hz which gives a maximum unam-biguous range of 8000 nmi. The format for these figures is similar to thatSused in Figures 2, 3 and 4 except for the very restricted doppler extent.Again each figure represents a 6.4-minute average. In this case the inco-herent average is composed of 30 separate integration periods of 12.8 secondseach. In each of the figures ground backscatter is visible from about 1200nmi to 1900 nmi. The near-range noise amplitude-range distribution undergoesthe same shifts in range as seen in previous figures. However, Figure 5shows a large amount of noise in the range 1300 to 1800 nmi which seems tobe multiplicative because its amplitude-range appears to correlate well withclutter amplitude-range. To investigate the source of this noise the 30integration periods which made up the 6.4-minute average were examined indi-vidually. Figure 8 shows the single integration time found to contain themultiplicative noise. Since the interruption of one transmit module couldcause a noise burst similar to this one, the indicators of transmitter statuswritten into the heade- on the raw data tape were examined. They showed noevidence of transmitter interruption. Figure 9 shows a two-minute averageon beam 13V and is included to indicate the appearance of long-term averageson beam 13, vertical which do not include the multiplicative noise bursts.Although this noise phenomenon may not be typical, it was included becauseit may represent one of the sources of far-range noise contamination. Sincethis did not represent a near-range phenomenon, it was not investigatedI further.

D. Antenna Elevation Patterns Derived from Meteor Data (U)

(U) In order to gain something more useful than the mere identificationof the near-range noise, which is considered to have been accomplished byshowing the gross shift in range as antenna elevation pattern is changed, themeteor data taken at 10 PRF and shown in Figures 5, 6 and 7 have been reducedto provide elevation antenna patterns of beam 13, both vertical and horizontalpolarization, and of the Yagi. From this data and assuming that the Yagiproduces its theoretical lobe-maximum gain and that the near-range noise ispredominantly meteors, a scattering coefficient ain for the meteor flux hasbeen calculated.

(S) Figure 10 shows the same data as was previously shown in Figure 5except that the signal level in each range cell has been reduced to a singlenumber. This was accomplished by separating the 10-Hz doppler extent availableinto 4 segments each 2.5 Hz wide. For each of 30 integration times a mediansignal level was determined for each segment. These four medians were thenaveraged over the thirty integration periods to produce a 6.4-minute average.

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Because the energy from the meteor returns has been seen to be rather wellspread over the 10-Hz doppler extent, the median is a good measure of signalstrength while eliminating CW and aircraft targets which would contaminate atotal power measure. The DC offset which appears at some frequency is elimin-ated by not including that segment covering zero frequency when finally com-bining the remaining three medians to produce a single measure of the s~gnalin each range cell.

(U) Before the signal levels shown in Figure 10 can be used to plotthe antenna elevation pattern, they must be normalized to remove the range-spreading factor. Figure 11 shows the factor used to normalize the receivedsignals to that expected from a distributed target at 200 nmi. Figure 12shows the relationship between slant range and elevation angle used to estab-lish the elevation angle. Figure 13 is the result of applying these twofigures to Figure 10 and plotting the signal levels relative to the maximum-• 'return which occurred at 280 nmi. The dB scale shown is half that used to

plot the data points thus showing one-way antenna gain. Antenna elevation Apatterns determined in this way assume the scattering coefficient for themeteor flux to be constant as a function of elevation angle. For the anglesbetween 40 and 250 which were used here this assumption probably does not dis-tort the skirts of the patterns very much. For this set of data, the angleextent over which the data are valid is from about 40 to about 250. The highangle limit results from the switching transient which contaminates the firstrange sample. The low angle limit results from an accumulation of spreadingloss, which reduces signals to levels comparable to the noise in the skipzone produced by other users.

(U) Figu-e 14 presents a measured elevation pattern for beam 12,vertical. The elevation pattern for beam 13 was not measured. This figureshows a peak at 9.50 which compares rather well with the peak derived fromthe meteor data and shown in Figure 13.

(U) Figures 15 and 16 show t'e raw median data and the derived eleva-tion pattern for beam 13, horizontal. Figure 17 shows the measured elevationpattern for beam 7. Again the beam 13, horizontal, pattern was not measured.The elevation pattern for beam 7, horizontal, is taken to be representativeof the antenna when operating horizontally polarized. A comparison of themeasured pattern with the one derived from the meteor data indicates arather good agreement in the position of the pattern nulls and an interest-ing deformation of the shape of the main lobe. Whether the deformation isreal or is an artifact introduced by this particular meteor data is unknown.Since the antenna gain in Figure 16 is plotted relative to the maximum gain

of beam 13, vertical, it is apparent from Figure 16 that the absolute gain -iof beam 13 is reduced by about 1 dB when using horizontal polarization.

(S) Figures 18 and 19 show the raw median data and the derived eleva-tion pattern for the Yagi. Measured azimuth patterns indicate that thebeamwidth for beam 13 at 23 MHz is about 60. The half-power beamwidth forthe Yagi has been measured to be about 360. If a single meteor trail were

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being examined, its radar cross section would not depend on antenna beam-width. How ver, since the averaged data represent the effects of on theorder of 10 meteors per range cell, the meteor flux must be considered anarea phenomenon. Solving the radar equation for the antenna gain G

G =(43 R4 pR\ 1/2

In this equation R is the range to the target, PR is the received power,is the wavelength, PT is the transmitted power, and a' is the target radarcross section. For distributed targets the radar cross section a is consid-ered in terms of the target area and a scattering coefficient representingthe radar cross section of a unit area. Thus

a =a°RB AR (4)

where co is the scattering coefficient and the area for this particularsituation is the resolution cell size. The resolution cell is formed by theantenna half-power beamwidth Bw (radians), the range to the target R, and therange resolution AR. Substituting equation (4) into equation (3)

(I )3 R3 PR 1/2

G =\2 0BR) (5)X2P (;BM AR

(S) From equation (5) it may be seen that although Yagi operation hasa factor of 6 decrease in transmit power, because the Yagi uses only one ofthe six. transmitter modules, this decrease is offset by a factor of 6 in-crease in antenna half-power beamwidth. Having made the corrections neces-sary to allow an absolute gain comparison between the Yagi and the systemantenna, note from Figure 19 that the maximum gain of the Yagi is about 4 dB iibelow the maximum gain for beam 13, vertical. If the theoretical gain ofthe Yagi of 19-dBi is realized, the system antenna gain is 23 dBi for 23 MHz.Gain for beam 13, horizontal works out to about I dB lower at 22 dBi. JU

(U) Figure 20 shows the Yagi elevation pattern courtesy R. Rafase. TrComparison of Figure 19, the elevation pattern derived from meteor data, with AFigure 20 reveals that the elevation patterns shown in the two figures agree -i-fairly well.

E. Determination of Scattering Coefficient for the Meteor Flux (U) 'B

(U) Equation (4) made use of a term ao which represented the radar crosssection per unit area for a distributed target. For earth backscatter thisfactor, ao, is about -17 dB. The meteor data taken as part of this test

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allows the calculation of a similar factor ao for the meteor flux. Figure

10 gives -120 dBm as the median signal level at the range where meteor

activity is strongest, 280 nmi. The meteor flux produces a radar return

that is spread rather uniformly over the entire 10-Hz doppler extent. The

signal processing used for this data divided the spectrum into 128 doppler

cells. Therefore, the equivalent coherent received signal is -120 + 21 or

-99 dBm. Solving equation (5) for ao the scattering coefficient

a0 = (4n) 3 R3 PR (6!•-0oo (6)

G2 x 2 Bw AR PT

where R is the range to the targ&, PR is the received power, G is the antenna

gain, X is the wavelength, BW is the half-power beamwidth (in radians), AR

is the range resolution and PT is the transmit power. Evaluating the equation

in dB gies PT = 96 dBm, PR = -99 dBm, G2 46 dBi, = 22.3 dBsm, (4)=

33 dB, R = 171 dB, BW = -9.8 dB, and AR= 45.7 dB. The scattering coeffi-

"cient Crm is then -94.8 dB. The data from which this coefficient was derivedwere taken during mid-March at about 0700 local time in beam 13.

(U) Certain cautions should be observed in using the meteor scattering

coefficient. Because the meteor is a diffuse or spread signaL rather than

a coherent return, the appropriate adjustxvants must be made for the signal

prccessing used. Thus if the spectrum extent occupied by the meteor returns

is divided into 128 doppler cells, the signal level calculated from a( must

be reduced by 21 dB. Diurnal and azimuthal variations of am are expected.

VI. CONCLUSIONS (U)

(S) Certainly sufficient evidence has been gathered to confirm that

for 23 MHz the near-range noise results primarily from line-of-sight meteor

trail reflections. To a lesser extent line-of-sight aircraft and a switchingi transient contribute to the "noise" in the very near range.

(S) For the lower operating frequencies, there are indications of the

possibility of spreading of surface wave clutter by antenna vibration. Fur-

ther testing is required to determine whether this is indeed the case. No [spreading of surface wave clutter above a clutter-to-noise ratio of 66 dB

was observed at 23 MHz.

(S) Antenna corona does not appear to be a factor above 10.5 MHz.

&i Corona existing below 10.5 MHz, because of its connection with television

interference, is the subject of an intensive continuing investigation which

will be reported separately.

(S) The absolute antenna gain for beam 13, vertical was estimated tobe 23 dBi. Various elevation patterns measured by Mr. Carmen Malagisi in

the summer of 1971 were confirmed. A scattering cross section, am for the

meteor flux was determined to be -94.8 dB.

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VII. RECOMMENDATIONS FOR FUTURE WORK (U)

(U) Much valuable information would be gained from a program to meas-ure the elevation pattern as a function of frequency for each of the beamsthat compose the system antenna. By making use of the meteor flux this maybe accomplished with about 10 minutes of system time for each patterndesired. An analysis of the variations in the elevation patterns betweenbeams and on different frequencies would be valuable in assessing the properfunctioning of the antenna itself.LJ (S) The propagation prediction program and the raytracing programs

currently use an idealized elevation pattern based on the assumption thatthe antenna system design goal of a frequency and beam-independent eleva-tion pattern had been met. Analysis of Mr. Malagisi's measured elevationpatterns supported by the patterns derived from meteor data indicates thatthis is a very bad assumption. Both the propagation prediction program andthe raytracing programs should be fitted with a more realistic model of theantenna elevation patterns.

(U) The indications of noise introduced by antenna vibration whenusing the lower operating frequencies should certainly be pursued by furthertesting.

VIII. ACKNOWLEDGMENTS (U)

(U) The author would like to acknowledge the assistance of CAPT MikePodhajecki who assisted in the data acquisition phase of the test. Thesignal processing routines used were written by Mr. James Hudnall withspecial modifications for signal averaging by CAPT Mark Clausen. The statis-tics routines used to determine median signal levels were supplied by Mr.Paul Shannon.

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REFERENCES

1. Joseph Parr, "Antenna Patterns, Project COBRA MIST," Volumes 1 and 2,Rome Air Development Center, July 1972, UNCLASSIFIED.

2. C. T. Home and G. H. Millwan, "The Characteristics of Overdense Meteorsat HF Backscatter Radar," Proceedings of the OHD Technical Review Meetingof 17-18 March 1971, Vol. I, SECRET.

3. 0. G. Villard, et al, "The Role of Meteors in Extended Range VHFIF Propagation," Proceedings of the IRE, October 1955, UNCLASSIFIED.

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MEMORAN]JJM

20 February 1997

Subj: fccuient Declassification

Ref: (1) Code 5309 Mexorandumr of 29 Jan. 1997(2) Distribution Staterents for Technical Publications

NRL/gJ/5230-95-293

Encl: (a) Code 5309 Memorandum of 29 Jan. 1997(b) List of old Code 5320 Reports(c) List of old Code 5320 Menorandum Reports

1. In Enclosure (a) it was recca-rended that the foll(wing reports be declassified,four reports have been added to the original list:

Fon-Tl: 5589t,5811, 58244 5825, 5849 5862, 5875, 5881, -5903,/ 5962, 6015V/6079,/6148, 6198, 6272 6371, 6476/6479( 6485/6507$6508, 6568/ 6590/ 6611,6731,6866,17044, 7051, 7059, 735077428, 7500, 7638, 7655. ?Ad 7684, 7692.V V'/ I. / / //v/ /Memo/ 1251, 1287 1316, 1422, IVM/1500, 15 2 7 ;/,15 3 7 , , 1 5 4 0 ,/ 1 5 6 7 , 1637 ,1647, ,1727, 1758, 1787 ,/l789,/1790/1811 1'817, 1823 Y1885, 1939, 1981, 2135, 2624,2701,2645/2721, 2722, 2723, 2766! Ad 2265,2715?/

The reccrended distribution statement for the these reports is: Approved forpublic release; distribution is unlimited.

2. The above reports are included in the listings of enclosures (b) and (c) andwere selected because of familiarity with the contents. The rest of these documentsvery likely should receive the same treatunent.

MHe:adrick

Code 5309

Code_ 121 ---- " ••Code 5300Code 5320Code 5324