Synthetic Aperture Radar - Advanced - Applied Technology Institute

Professional Development Short Course On: Advanced Synthetic Aperture Radar Instructor: Barton D. Huxtable, Ph.D

ATI Course Schedule: ATI's Synthetic Aperture Radar:

http://www.ATIcourses.com/schedule.htm http://www.aticourses.com/advanced_synthetic_aperture_radar.htm

349 Berkshire Drive • Riva, Maryland 21140 888-501-2100 • 410-956-8805 Website: www.ATIcourses.com • Email: [email protected]

Synthetic Aperture Radar Fundamentals

Advanced

May 4-5, 2009

May 6-7, 2009

Chantilly, Virginia

Chantilly, Virginia

Instructors:

Instructor:

Walt McCandless & Bart Huxtable

Bart Huxtable

$1290**

(8:30am - 4:00pm)

$990 without RadarCalc software

$1290**

(8:30am - 4:00pm)

$990 without RadarCalc software

**Includes single user RadarCalc license for Windows PC, for the design of airborne & space-based SAR. Retail price $1000.

What You Will Learn • Basic concepts and principles of SAR. • What are the key system parameters. • Performance calculations using RadarCalc. • Design and implementation tradeoffs. • Current system performance. Emerging systems.

What You Will Learn • How to apply SAR to the design of highresolution systems. • How to design and build high performance signal processors. • Design and implementation tradeoffs using RadarCalc. • SAR activities in DoD, NASA and commercial applications. • Current state-of-the-art.

Course Outline

Course Outline

1. Applications Overview. A survey of important applications and how they influence the SAR system from sensor through processor. A wide number of SAR designs and modes will be presented from the pioneering classic, single channel, strip mapping systems to more advanced all-polarization, spotlight, and interferometric designs. 2. Applications and System Design Tradeoffs and Constraints. System design formulation will begin with a class interactive design workshop using the RadarCalc model designed for the purpose of demonstrating the constraints imposed by range/Doppler ambiguities, minimum antenna area, limitations and related radar physics and engineering constraints. Contemporary pacing technologies in the area of antenna design, on-board data collection and processing and ground system processing and analysis will also be presented along with a projection of SAR technology advancements, in progress, and how they will influence future applications. 3. Civil Applications. A review of the current NASA and foreign scientific applications of SAR. 4. Commercial Applications. The emerging interest in commercial applications is international and is fueled by programs such as Canada’s RadarSat, the European ERS series, the Russian ALMAZ systems and the current NASA/industry LightSAR initiative. The applications (soil moisture, surface mapping, change detection, resource exploration and development, etc.) driving this interest will be presented and analyzed in terms of the sensor and platform space/airborne and associated ground systems design and projected cost.

1. SAR Review Origins. Theory, Design, Engineering, Modes, Applications, System. 2. Processing Basics. Traditional strip map processing steps, theoretical justification, processing systems designs, typical processing systems. 3. Advanced SAR Processing. Processing complexities arising from uncompensated motion and low frequency (e.g., foliage penetrating) SAR processing. 4. Interferometric SAR. Description of the state-ofthe-art IFSAR processing techniques: complex SAR image registration, interferogram and correlogram generation, phase unwrapping, and digital terrain elevation data (DTED) extraction. 5. Spotlight Mode SAR. Theory and implementation of high resolution imaging. Differences from strip map SAR imaging. 6. Polarimetric SAR. Description of the image information provided by polarimetry and how this can be exploited for terrain classification, soil moisture, ATR, etc. 7. High Performance Computing Hardware. Parallel implementations, supercomputers, compact DSP systems, hybrid opto-electronic system. 8. Image Phenomenology & Interpretation. Imagery of moving targets (e.g., train off the track), lay over, shadowing, slant-plane versus ground plane imagery, ocean imagery. 9. Example Systems and Applications. SIR-C, ERS-1, AirSAR, Almaz, image artifacts and causes. ATR, coherent change detection, polarimetry, alongtrack interferometry.

Register online at www.ATIcourses.com or call ATI at 888.501.2100 or 410.956.8805

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349 Berkshire Drive Riva, Maryland 21140 Telephone 1-888-501-2100 / (410) 965-8805 Fax (410) 956-5785 Email: [email protected]

The Applied Technology Institute specializes in training programs for technical professionals. Our courses keep you current in the state-of-the-art technology that is essential to keep your company on the cutting edge in today’s highly competitive marketplace. Since 1984, ATI has earned the trust of training departments nationwide, and has presented on-site training at the major Navy, Air Force and NASA centers, and for a large number of contractors. Our training increases effectiveness and productivity. Learn from the proven best.

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The Need for SAR Image Processing

Advanced SAR Processing

Optical Data

To ApplicationSpecific Processing

SAR Image Formation Processing

SAR Data To ApplicationSpecific Processing

Advanced SAR Processing

Synthetic Aperture Image Formation

kazimuth

Fou rier

Tran sfor

m

Image

Measured Fourier Components of Imaged Region

krange

Advanced SAR Processing

Born Approximation •

Electromagnetic scattering theory gives the following leading order approximation

E (r ) ~ eik incident ⋅r

eikr + f k (r$ ) r

f k ( k$ scattered ) ~ ∫ ei( k incident − k scattered )⋅x ε ( x ) dx ⇒The scattered radar waves measure the Fourier transform of the target (dielectric inhomogeneity) - Fourier transform wavevector is the bistatic scattering vector kincident-kscattered

Matched-Filter on an Undersampled Signal

Ambiguity

Advanced SAR Processing

Range-Doppler Algorithm Phase Phase History History Data Data

Multiply by Range Matched-Filter

Corner Turn SAR SAR SLC SLC Image Image

Range Curvature Interpolation

Advanced SAR Processing

Multiply by Doppler Matched-Filter

Advanced SAR Processing

Range-Doppler SAR Image Formation •

Doppler (or azimuth) compression - Apply azimuth (or along-track or slow-time) matched-filter to the range-compressed phase history - Recall that the correlation of two matched chirps produces an impulse ⎛ (ξ − x )2 ⎜ ⎜ R + y' ⎝

⎞⎫⎪ ⎟⎬d range_compressed ( t , ξ)dξ ⎟⎪ ⎠⎭ ⎧ ⎧⎪ 2ω0 ⎛ (ξ − x )2 ⎞⎫⎪ 2ω ⎛ R + y' ⎞ ⎜ ⎟⎬ exp⎪⎨2πi 0 = δ rg ⎜ t − ⎟ ∫ exp⎨− 2πi c/2 ⎠ c ⎜⎝ R + y' ⎟⎠⎪⎭ c ⎪⎩ ⎪⎩ ⎝ ⎛ R + y' ⎞ ≅ δ rg ⎜ t − ⎟δ az (x − x ') c / 2 ⎝ ⎠ ⎧⎪ 2ω 0 exp 2 i − π ∫ ⎨⎪ c ⎩

•

•

⎛ (ξ − x ')2 ⎜ ⎜ R + y' ⎝

⎞⎫⎪ ⎟⎬dξ ⎟⎪ ⎠⎭

Thus, the target energy has been localized to the correct (t,x) location - t = (R+y’)/(c/2) - x = x’ Linearity generalizes this point-target discussion to formation of an extended image

SAROS Raw Data

Advanced SAR Processing

Range Geometry of Motion Errors

Advanced SAR Processing

ζ actual location δζ

η δη nominal location

H

R

Rnominal

Ground: flat uneven

⎧ 2 ⎛ ⎞ 2 2 2 ⎪⎪R j − H + ⎜ R j − (H + δζ k ) − δηk * look ⎟ ⎝ ⎠ ∆R j = ⎨ ⎪ 2 2 ⎪⎩R j − R j − δζ k + (− δηk * look )

(

)

for R j > H + δζ k for R j ≤ H + δζ k

Minimum Antenna Area Constraint •

•

Advanced SAR Processing

SAR antenna is the key subsystem determining the performance of a SAR - Antenna design affects swath width, azimuth resolution, range and azimuth ambiguity level, and clutter- and signal-to-noise ratios Ambiguity constraints determine the minimum antenna area for a SAR

Aantenna ≥ AMIN

4 vλ R = tan ϕ i c

- Note that there is very little freedom to alter AMIN - Practical designs typically are twice or more this area to suppress ambiguities

Seismic Migration Algorithm in four elegant steps

Advanced SAR Processing

Step 1: Fourier transform the range compressed[1] phase history data D (κ , ω ) = ∫∫ exp{− 2πi (ωτ + κξ )}d (ξ ,τ )dτdξ Step 2: Interpolate the transformed phase history 2 ⎛ c⎡ 2 2⎤⎞ ⎛ ⎞ ⎛ c ⎞ D' ⎜ k x , k y ⎟ = D⎜⎜ k x , ⎢ ⎜ + k y ⎟ + k x2 − ⎥ ⎟⎟ λ ⎥⎟ ⎜ 2⎢ ⎝λ ⎝ 2 ⎠ ⎠ ⎣ ⎦ ⎠ for range curvature. ⎝ This is the so-called “Stolt interpolation,” which effectively corrects Step 3 Multiply the interpolated, transformed phase history by a phase factor 2 ⎧ ⎡ ⎛2 ⎤ ⎫⎪ ⎛ 2 c ⎞ ⎪ ⎞ I(k x , k y ) = exp⎨− 2πiR 0 ⎢ ⎜ + k y ⎟ + k 2x − − k y ⎥ ⎬ D' ⎜ k x , k y ⎟ λ 2 ⎠ ⎢ ⎝λ ⎥⎪ ⎝ ⎠ ⎪⎩ ⎣ ⎦⎭ This is effectively the azimuth matched-filter. Step 4 Inverse transform the Fourier transform of the image

i ( x, y )image. = ∫∫ exp{+ 2πi (k x x + k y y )}I (k x , k y )dk x dk y which produces the complex Fine Points Range compression may conveniently be done by multiplying D(κ,ω) by the complex conjugate of the range reference function[2] in Step 1. Windows, spectral filters, equalization factors, etc., may be multiplied onto I(kx,ky) or D(κ,ω) anywhere between the Fourier transforms in Steps 1 and 4. This enables custom shaping of the impulse response, compensation of antenna patterns, transmit pulse equalization, etc. [1] “Range compressed” phase history data because we don’t want to mix in any phase modulation included with the transmit pulse, e.g., the quadratic phase of a chirped pulse. [2] The range reference function is the Fourier transform of the transmitted pulse.

Advanced SAR Processing

SAR Image Geolocation •

SAR image pixel location Rpixel determined as a solution to three equations - range equation

Rslant range = R SAR − R pixel - Doppler equation

f Doppler centroid =

2

λ Rslant range

(V

Vpixel = ω Earth × R pixel - Earth model equation

R pixel = REarth + h

SAR

) (

− Vpixel • R SAR − R pixel

)

AirSAR Layover Example

Advanced SAR Processing

Scattering Matrix Phase Calibration • •

Advanced SAR Processing

The 4 channel image data are used to construct a scattering matrix at each pixel A measured scattering matrix for a fully polarimetric SAR is:

⎛ Shh exp j (φ t + φ r ) Shv exp j φ r ⎞ R = exp j (φ t,v + φ r,v )⎜ ⎟ S vh exp j φ t S vv ⎠ ⎝

•

•

where Sij is the complex amplitude for the j-transmitting i-receiving polarization and φt and φr are the phase factors for transmit and receive. (φt = φt,h- φt,v) and (φr = φr,h- φr,v) Two assumptions are used to calculate the difference in transmitted and received phase - hv = vh amplitudes for backscatter systems (averageing across the image produces a φt - φr expression) - knowledge of the predicted phase difference in the hh and vv signals in order to determine φt - φr - possibly given by a corner reflecting target R (with relative phase) is known after solving for φt and φr

Advanced SAR Processing

Baseline Decorrelation – Spectral View k ground =

2 BW sinθ c

sin θinc λ/2

θM

θs

k

2ω cosθ ∆θ c

Bcritical = R ∆θcritical = R

λR 2BW sin θ c = c 2ω cos θ δ rg cos θ

Ground Wavenumber Filtering

After Filtering

Before Filtering

Advanced SAR Processing

Advanced SAR Processing

DPCA • •

Doppler of ground clutter is primarily due to motion of the radar ⇒ Try to “stop” the radar so it behaves like a conventional MTI radar Implement with a Displaced Phase Center Array Phase Centers

Time

Pulse n+1

Pulse n

Pulse n-1

R

R T

R

R T

R

R T

Antenna Path

+

Σ -

Conventional MTI signal

Ground Moving Target Indication (GMTI)

J er np Tur sey ike

Range

95

New

I-2

1 sq-km Azimuth 100 kph

Advanced SAR Processing

Boost Your Skills with On-Site Courses Tailored to Your Needs The Applied Technology Institute specializes in training programs for technical professionals. Our courses keep you current in the state-of-the-art technology that is essential to keep your company on the cutting edge in today’s highly competitive marketplace. For 20 years, we have earned the trust of training departments nationwide, and have presented on-site training at the major Navy, Air Force and NASA centers, and for a large number of contractors. Our training increases effectiveness and productivity. Learn from the proven best. ATI’s on-site courses offer these cost-effective advantages: • You design, control, and schedule the course. • Since the program involves only your personnel, confidentiality is maintained. You can freely discuss company issues and programs. Classified programs can also be arranged. • Your employees may attend all or only the most relevant part of the course. • Our instructors are the best in the business, averaging 25 to 35 years of practical, realworld experience. Carefully selected for both technical expertise and teaching ability, they provide information that is practical and ready to use immediately. • Our on-site programs can save your facility 30% to 50%, plus additional savings by eliminating employee travel time and expenses. • The ATI Satisfaction Guarantee: You must be completely satisfied with our program.

We suggest you look at ATI course descriptions in this catalog and on the ATI website. Visit and bookmark ATI’s website at http://www.ATIcourses.com for descriptions of all of our courses in these areas: • Communications & Computer Programming • Radar/EW/Combat Systems • Signal Processing & Information Technology • Sonar & Acoustic Engineering • Spacecraft & Satellite Engineering I suggest that you read through these course descriptions and then call me personally, Jim Jenkins, at (410) 531-6034, and I’ll explain what we can do for you, what it will cost, and what you can expect in results and future capabilities.

Our training helps you and your organization remain competitive in this changing world. Register online at www.aticourses.com or call ATI at 888.501.2100 or 410.531.6034