The probability of detecting and tracking RADAR targets in clutter at low grazing angles

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The probability of detecting
and tracking RADAR
targets in clutter at low
grazing angles
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by the/an author.
Additional Information:
• A Doctoral Thesis. Submitted in partial fulfilment of the requirements
for the award of Doctor of Philosophy at Loughborough University.
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"THE PROBABILITY OF DETECTING AND TRACKING
RADAR TARGETS IN CLUTTER AT LOW GRAZING ANGLES"
BY
R W HADOO,I OBE, AFM, MSc CEng MIERE MRAeS
A DOCTORAL THESIS
,
Submitted in partial fulfilment of the re~uirements
for the award of
Doctor of Philosophy of the Loughborough University of Technology
30
September 1982
@ R W HADDOW 1982

-------------~---
CERTIFICATE OF ORIGINALITY
This is to certify that I am responsible for the work
submitted in this thesis, that the original work is my own
except as specified in acknowledgements or in footnotes, and that
neither the thesis nor the original work contained therein ha.s been
submitted to this or any other institution for a hl.gher degree.
"It is probably safe to say that clutter will
never be understood completely because there
. are so many variables to control "
TOMLINSON
CONTEN'fS
Preface and Acknowledgements
1
Abstract ii
Index to Chapters iii
Glossary of Terms and Symbols X
PART I
Chapter l. The Nature of Radar Clutter
2. Terrain Modelling
3. Volume Clutter - Atmospheric' and Rain Effects
4. Surface Clutter - Terrain
5. Non-Stationary Clutter - l{ind, Air Turbulence,
Chaff and Birds
6. Radar System and Target Detection Parameters
7. Diffraction
8. Propagation - Refraction and .Reflection
9. Multipath
10. Clutter Variation with Terrain Slope
11. System Performance Assessment Model
12. Summary of Research and RecoID..'1lcndat'ions
Annexes:
A. Statistical Distribution for Fluctuating Radar
Signals
B. Received Clutter Power from Resolution Cell
and Reflectivity Coefficients
C. Fresnel-Kirchoff Single Knife-Edge Diffraction
Solution
D.' Computer Programs and Flow Charts
E. Low Level Tracking Errors and Track Length Probability
F. Illuminated Surface Areas and Terrain
Curvature
G. Applications of Model to Example System and
Location
H. Application of Model to Example System and
Location (Classified Secret)
Appendices to Part I
1 (Annex A) \vei bull Shape Para'lleter Correlation
1 (A'1nex F) Statistical Analysis to obtain a Distributed
Clutter model over Sloped Terrain
PAIlT II
Radar Performance Bibliography
PREFACE
This report was compiled as a part-time study during the author's appointment
as Guided Weapon Specialist at the Department of Air Warfare at Royal Air
Force College Cranwell. Although sponsored by the Ministry of Defence the
results and opinions are those of the author and should not be taken as
official.
ACKNOWLEDGEMENT
Gratitude is expressed to Dr J E Hudson and to Professor J W R Griffiths for
. the opportunity and assistance in pursuing the research.
Thanks are also due to Mr J S Nicholson of the RAF College Mathematics
Department and especially to Mr D Clarke Trenchard Hall Librarian, whose efforts
even exceeded·the considerable resources of MIT in uncovering associated
literature.
Assistance received from the Royal Armament Research and Development, Royal
Signals and Radar, and Admiralty Surface Weapons Establishments, Hunting
Engineering and particularly British Aerospace Dynamics is most gratefully
acknowledged; as is the financial sponsorship of the Ministry of Defence.
Finally the time-consuming survey and data tabulation effort alone could not
have been completed as a part-time task without the support of an understanding
family - who have somehow withstood five such tasks in a decade - interspersed
with an ever increasing external lecturing commitment at home and abroad.
i
ABSTRACT
Moaern military acquisition and tracking raaars are required to operate
against aircraft and missiles specifically designed to have minimal
radar cross section (RCS) and which fly at very low level to take
maximum advantage of terrain screening.
A model for predicting system performance is necessary for a range of
terrain types in varying precipitation and seasonal cultural conditions.
While the main degradation is from surface clutter and denial of sightline
due to terrain and other local obstructions, several other factors such
as multipath propagation, deliberate jamming and even operator performance
contribute to the total model. The possibility that some radars may
track obscured targets, however briefly, by using the diffraction path,
is of particular interest.
Although this report critically examines each of the contributory factors
in order to select optimum values for inclusion in an overall computer
prediction model; a new surface clutter model is specifically developed
for sloped terrain using actual clutter measurements. The model is
validated by comparison with an ~xtensive survey of worldwide clutter
results from both published and unpublished sources.
Certain constraints have been necessary to restrict the study to a
manageable size, while meeting the requirements of the sponsors.
Attention is therefore focussed upon performance predCc.tion for
typical mobile tracking radar systems designed for operation against
small RCS low level targets flying overland.
INDEX (TO PAH,], I)
CHAPTER 1 - THE NATURE OF WlDAR
CLm'~'r:H
l'orms of Clutter
Research Parameters 1-3
·Clutter Variables 1-4
Statistical Distributions 1-5
Clutter Reliability and Repeatability of
Clutter Measurements 1-6
Review of Clutter Research 1-7
Problem Areas 1-10
Aims of the Study 1-11
CHAPTER 2 - TERRAIN MODELLING
Earth's Surface Model 2-13
Sight-Line 2-14
Terrain Spot Heights 2-15
Earth's Curvature and Intervisibility 2-15
Grazing Angles and Beamwidth Effects 2-17
Resolution Cells 2-19
Slope of Surface Resolution Cell 2-20
Terrain Data Base 2-21
Screening Diagrams 2-23
Intervisibility Plots 2-25
Chapter Summary 2-27
CHAPTER 3 - VOLUME CLUTTER - RAIN AND ATMOSPHERIC EFFECTS
Rain and Cloud Attenuation 3-45
Cloud and Fog 3-46
Rain Reflectivity 3-48
iii