high resolution radar technology
TRANSCRIPT
High resolution radartechnology for
environmental applications
Dr Richard HollidayDr Duncan Wynn
Matt-Rhys Roberts
• Introduction
• Survey methods- manual- LIDAR/hyper-spectral, thermal imaging- RADAR/ real-beam mapping/SAR, interferometric SAR
• Overview of high resolution radar
• Environmental applications- mapping- remote sensing and surveillance- pollution monitoring
Content
Introduction
• A major threat to global stability is the change in the Earth’s climate
• Extremes of heat and drought, storms, wind, rain and more intense cold
• Unpredictable environmental behaviour- Temperature rises are likely to be non-uniform across the globe
• Uncertainty of the impact is incorporated into long-term national and international decision-making
- reflected in environmental standards and targets including :
- protection of people, homes and business from risk of flood- ensure availability of suitable water for drinking and bathing- prevention of destruction of natural habitats and extinction of animal species
- There is a very wide breadth of environmental issues …..
Climate change .. evidence
Winter and Summer rainfall rates 1766 to 1991
• Better understanding of the complex interaction between the Earth’s surface and atmosphere is essential
• Accurate descriptions of local and regional surface features and associated phenomena with timely monitoring are vital
Introduction
Survey methods
• The quality of surface maps is gauged primarily by the ability ofthe survey method and sensor to resolve closely spaced features…. generally defined in terms of resolution
Historically, surface feature (map or topographic) data has beenobtained by manual survey methods
• Autonomous- surface based- airborne
• Wide variety of methods- traditional survey, laser based, GPS based- passive samplers, ultrasonic gauges etc
• Labour intensive• Time consuming … untimely data/latency ?• Poor spatial coverage• Low spatial resolution – point sensors/measurements • Invasive – perturbation of measurement environment• Limited by accessibility of environment - ad-hoc methods such as General Quality Assessment (GQA for rivers) • Inaccurate and inconsistent – requires accreditation and standardisation
• Autonomous survey solutions are required ….
Survey methods : Manual
• Time consuming … untimely data/latency ?• Poor spatial coverage• Low spatial resolution – point sensors/measurements• Invasive – perturbation of measurement environment• Limited by accessibility of environment• Inconsistent – requires accreditation and standardisation
Survey methods : Automatic flow monitoring
Survey methods : Airborne
• LIght Detection And Ranging (LIDAR) • Wide area coverage – typically 600 m swathe width at 800m altitude• Measurements every 2m with resolution between 1m and 10m
• Compact Airborne Spectral Imager (CASI) • Thermal imager / daylight camera
Disadvantages of LIDAR
• High operating costs (> £10k / hour)
• Not all-weather performance- ineffective during heavy rain and/or low cloud/mist- degraded at high Sun angles and reflections
• Latency – data not processed locally (Coventry airport/OS)
• Unreliable for water depth (< 2m) and breaking/turbulent waves
• Lack of foliage/vegetation penetration
Survey methods : Real-beam mapping radar
• Wide area coverage – surface, airborne / satellite borne
• All-weather capability
Real-beam mapping radar
X-band (10 GHz)1° beamwidth
100m range resolution
Ludlow
Hereford
X-band (10 GHz) radar and video based measurements from a traffic scene (circa 1968)
Real-beam mapping radar
77 GHz radar and video based measurements from a traffic scene (circa 1998)
Survey methods : Synthetic Aperture Radar (SAR)
• Wide area coverage – airborne / satellite borne
• All-weather capability
• Costs- Capital costs
typically >£100 k excl. aircraft installation and maintenance> £1m for satellite payloads
- Operating costs typically > £10k / hour
Synthetic aperture radar (SAR): Airborne
X-band (10 GHz)1° beamwidth
0.3m range resolution
Synthetic aperture radar (SAR): Satellite-borne
TOPEX/POSEIDON ocean topography project
Disadvantages of microwave real-beam and SAR radar
• SAR imagery is prone to distortions, obscuration and RF interference
• Lack of foliage/vegetation and surface penetration
• Speckle cancellation is required
• Latency – data not processed locally - Time dependent phenomena are not imaged
• Moving object detection with MTI radar modes
• Lack of availability
• Ownership of data
• Cost
Distortion of SAR imagery
Optical and SAR view of same airfield
Obscuration of SAR imagery
Effect of RF interference upon SAR imagery
High resolution radar for environmental applications
High resolution radar operating modes
• High resolution mapping
• Velocimetry
• Target classification - Polarimetry- Non-cooperative Target Recognition (NCTR)
• Bathymetry
Outline radar specification (target)
Modes: High resolution surface mapping (2D and 3D)Velocimetry max. velocity < 15 m/s (33 mph / 54 km/hr)Bathymetry < 2m water depthClassification / non-cooperative target recognition
surface texture, birds, insects, humans
Coverage: 360° azimuth, ± 40° elevation
Resolution: spatial < 0.03m (range), < 0.05m (azimuth) at 300m velocity < 0.003 m/s or ±0.01% max. velocity
Sensitivity: > 10 dB SNR at 5 km against 1m2 non-fluctuating, stationary target
Polarisation: Fully polarimetric
Physical: weight under 80 kgmaximum size 1m x 1m x 1m
Integral navigation unit including GPS and INS
High resolution radar
• Angular resolution (related to antenna beamwidth and physical size)improves at millimetric/sub-millimetric wavelengths
… but atmospheric attenuation is worse
10-2
10-1
100
0
5
10
15
20
25Beamwidth vs antenna dimension
Dimension (m)
3d
B b
ea
mw
idth
(d
eg
)
3dB beamwidth of 1m antenna is typically 1° at 94 GHz
High resolution radar : Atmospheric attenuation94 GHz
150 GHz“windows”
High resolution radar
• Radar technology at millimetric/sub-millimetric wavelengths is more affordable • Hardware at millimetric/sub-millimetric wavelengths is physically small
…. portable and hand-held equipment is convenient
Slot antenna
High resolution radar
• Portable high resolution radar is able to exploit improved geometry to overcomedistortion and obscuration
• Multiple radars can be networked for simultaneous coverage
• Surface based measurements underneath tree-canopies overcome foliage and vegetation shielding
• RF electromagnetic spectrum is sparsely occupied at millimetric/sub-millimetric wavelengths … very low probability of RF interference
High resolution radar
102
103
104
-20
0
20
40
60
80
100
120SNR vs Range
Range (m)
SN
R (
dB
)
• 10 dB SNR against 1m2 non-fluctuating target at 5.5 km with RF transmitter input power 50 mW
• >5% RF bandwidth at 94 GHz for better than 0.5 m range resolution
• Multi-frequency RF transmission to mitigate multipath
Typical radar performanceTarget RCS 1m2, radar height 1m
Velocimetry
Radar position B
Radar position A
VA
V(n)
A
Reference
A
Resolution celln
VN(n)
VE(n)
VD(n)
V(n)=VN(n)+VE(n)+VD(n)Measured radial velocity VA of resolution cell n, projected at angle A A
Velocity vector of resolution cell, n
• Determination of velocity vector of scattering centre within resolution cell by separate or multiple radar measurements
Classification: Polarimetry
• Radar returns are polarisation dependent – offers best opportunity for classification
• A fully polarimetric high resolution radar will record four separate complex reflectivities for the same scene
• Radar image texture can be interpreted as environmental features such as trees, hedges, fields (bare soil and vegetation), hills, ditches, bridges, shadows,buildings, roads, rivers and fences
• Texture can be measured by RCS of clutter CDF and moments of distribution
• Discrimination between type of vegetation is possible
• Close interaction with surface with topology data - roughness and soil moisture retrieval are possible
Classification: Non-cooperative Target Recognition (NCTR)
• Radar cross-section is enhanced by large number of point scatterersat millimetric wavelengths
• Scattering centres are discernible from measurements with high spatial and temporal resolution
• RCS is dependent upon aspect angle to radar
• Target motion compensation and RCS database collation is effective
• Target classification algorithms are widely available, such as template matching
• Target motion can be exploited with Inverse Synthetic Aperture (ISAR) imaging
Bathymetry
• Water depth can be determined from measurements of surface water wavelengths, directions and velocities
… requires high spatial and temporal resolution
X
Y
Bathymetry
• Combined with velocimetry
High resolution radar architecture
FMCW radar
Foster scanner antenna94 GHz FMCW radar
High resolution radar
-80 -60 -40 -20 0 20 40 60 80-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
Angle (deg)
Re
l. C
o-p
ola
r G
ain
(d
B)
Typical antenna radiation pattern 94 GHz co-polar
3 dB beamwidth 0.1o
Super-resolution
• Resolution limit defined by classical Rayleigh criterion can be improved by a factor of between 2 and 3
• Facilitated by :
- rapid update rates- stable antenna scanning (> 400 rpm)
- advanced signal processing- MUSIC / IMP / MAP algorithms
Super-resolution
Environmental applications : Mapping
• Land topography, elevation modelling and height contour plots
• Land cover classification, landscape and habitat survey- model validation to link land use with soil type and erosion prediction- crop and animal stock monitoring and grazing management for sustainable farming
• Road survey and highway mapping
• Flood plain surveys (with/without flooding)
• Surface water mapping including rivers, streams, canals, sewers- water flow rates, direction and depth monitoring, bathymetric mapping - identification and tracking of dissimilar bodies of water- mapping of mixing zones, outfalls and rivers
• Inter-tidal vegetation mapping
• Coastal erosion, tidal action and geomorphology
Environmental applications : Remote sensing and surveillance
• Monitoring of water abstraction and discharges for review of permits
• Meteorological measurements of fog, cloud and precipitation including ice particle size, internal circulations in fair weather, drop size distributions in rain and drizzle in shallow continental stratus cloud
• Wind speed and direction, storm direction, cloud base and cloud top detection
• Bird, insect and wildlife monitoring as a measure of water and environmental quality in conjunction with control measures
• Ecological surveys including number and distribution of specific wildlife (bird) species • Personnel and livestock location and identification
• Fire and smoke monitoring of forested areas
Environmental applications : Pollution detection
• Water detritus content warning- litter, oil, surface scum, foam, sewage fungus, ochre, buoys, floats, jetsom/flotsom
• Pollution monitoring of water reservoirs
• Air quality monitoring- Open-path monitoring from 10 m to over 1 km - detection and tracking of aerosols, airborne particulates (smoke), atmospheric absorption- detection of gaseous compounds in ambient air