algorithm architecture for synthetic aperture radar (sar ...kuang/lm/031014.pdf · algorithm...

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ASU MAT 591: Opportunities in Industry!

Algorithm Architecture for Algorithm Architecture for Synthetic Aperture Radar (SAR) Synthetic Aperture Radar (SAR)

Ground ProcessingGround Processing

Gary A. Mastin, Ph.D.Lockheed Martin Management & Data Systems

Intelligence, Surveillance, and Reconnaissance SystemsLitchfield Park, Arizona

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Overview

! SAR Processors - History! Driving Algorithm Functions - Review! Algorithm Architecture vs. Computer Architecture! Discussion Question

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In The Beginning…

GEMS Precision Optical Correlator

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The Advent of Digital Electronics

HIRSADAP

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The Benefits of the 1960s Space Program

! The advent of Digital Image ProcessingDigital Image Processing technology! The problem:

– We needed pictures of the moon’s surface for selecting landing sites– If the imaging spacecraft couldn’t return to earth, image capture by film

wasn’t possible– Late 1960’s television technology was power hungry, heavy, and bulky,

but the pictures were pretty good. (Yes, black & white images are good!!!!)

– Size, power, and weight constraints limited what we could launch– We didn’t have the communications bandwidth to broadcast live video to

the earth from the spacecraft

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The Benefits of the 1960s Space Program

! The solution:– Send lower-quality cameras into space to meet the size, power, and

weight constraints– Characterize the camera deficiencies prior to launch– Turn the video image into a grid of numbers representing intensity

onboard the spacecraft. Buffer the data on board, then dump it over the communications link as fast as possible … preferably before crashing into the moon’s surface!

– Treat images like large mathematical matrices! Use computers on the ground to correct the camera deficiencies after data receipt.

– While we are at it, lets also correct for contrast … and for motion blurs … and for perspective … and, hey, this is pretty powerful stuff!!!

! Other applications– Medicine– Defense " Synthetic Aperture Radar

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Advent of the “Mini-Computer”

! The Digital Equipment Corporation (DEC) PDP-series made computing affordable– PDP 8, PDP 10– PDP 11/45 # Big step forward

$ ~256 KB of core memory$ Video terminal for input instead of cards or paper tape$ Attached disk, 10s of MB per disk pack (multiple platters)$ 800 bpi 9-track tape for archive$ RSX 11M operating system supported multiple tasks$ Efficient DEC Fortran compiler, assembler, editor, linker, loader…$ Interface to peripherals

! Video monitors with disk buffers or even core. Dedicated image display functions! ! Fixed-point and floating-point FFT hardware

! For $250,000 to $750,000, a department or a small company could have its own image processing system.

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DEC VAX 11/780 – The Workhorse of 1980s

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Early Digital SAR Image Formation System

! Systems like the VAX 11/780 were augmented with peripherals for SAR data input, algorithm processing, and display

VAX 11/780System

Floating PointSystemsAP-120B

Array Proc.

ComtalDigital Image

Processor

DunnCamera

Phase HistoryFilm Digitizer

DCRSIHigh DensityDigital Tape

1600 bpi9-Track

Tape

VidiconCameraInput

OutputProcessing

VideoDisplay

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SAR Processing Algorithms

! With the flexibility of programming in compiled languages came algorithm innovation " “Simple” Matter of Programming

! Nomenclature

+1 -1

Forward Inverse

Fourier Transforms

Interpolation Filters

IPF In-Plane

Filter

CPF Cross-Plane

Filter

CPF Complex Array

Filter

c c c r

RFG_CC RFG_CR

Reference Function Generators

Corner Turn

CTM

DET

Magnitude Detect

DFC Data Format Conversion

OFR Output Format

Data I/O

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Modern Spotlight SAR Algorithm

cr

cr

Lin-Log

DFC

Range Deskew

IPFCPF

cr

AzRipple Corr.

Polar Tap

Range Taylor Wt.

RangeComp.

AzComp.

Complex Image Tap

CTM#

Polar Reformat

DET

Deskew Phase Change

# For multiple ingest, this becomes an out-of-memory transpose.@ Global. Based upon all data.

Multiple Ingest Flow: Vector Subset Loop

Vector Subset Loop (continued) Range Subset Loop

Range Subset Loop (continued) Remap Loop

Remap @

2

6 7 9

13 14 15 19

20

FFT1

RFG2A RFG2B

FFT2

CAF

RFG4 FFT3 CTM1 FFT4

RFG6

12

8

Range Ripple Correction

cc

11 Complex Array Filter

cr

AzTaylor Wt.

18RFG5

23 Magnitude Detect

27LLELLE

OFR128

Data Format Control

Output Format

Chain 1

Chain 2 Chain 3

Chain 4

-1 +1

-1-1

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Synthetic Target Phase History Generator

Syntarg

16 WriteSubset

17 ReadSubset

25 WriteSubset

26 ReadSubset

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Key SAR Processing Functions

! Dechirp and Range Deskew

Near Range Return

Center Range Return

Far Range Return

Dechirp Reference

Far Range Receive Pulse

Near Range Receive Pulse

fc

InstantaneousTransmit Freq.

Freq. AfterDechirp

BIF Time

Time

A/D Interval

Tp

B

TransmitPulse

t = 0

2Ra/c –∆r/c Tp 2∆r/c

Before Dechirp

After Dechirp

SkewAdapted from SpotlightSynthetic Aperture Radar:Signal Processing AlgorithmsBy W. Carrara, R. Goodman,R. Majewski, Artech House, 1995.

Scene CenterReceive Pulse

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Length of AnnulusDetermined byRadar Bandwidth

Annular ExtentOf Data AnnulusDetermined byCollection Time

Collection Surface(Slant Plane)Radial Position

Of AnnulusDetermined byRadar Center Frequency

λπ4

Ψ

Adapted from Spotlight SyntheticAperture Radar: A Signal ProcessingApproach by Jakowatz, Wahl, Eichel,Ghiglia, and Thompson

Fourier Reflectivity Space

Radar Depression AngleThat Determines theSlant Plane

θ∆

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! Polar Format Processing (Polar Reformatting)

Input Sample Output Sample

Azimuth Frequency Direction

Ran

ge F

requ

ency

Dire

ctio

n

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! 2-D FFT

Con

tiguo

us A

ddre

sses

"“N

”sa

mpl

es/v

ecto

r

Dire

ctio

n of

1-D

FFT

"

“M” Vectors "

Corner Turn(Transpose)

Dire

ctio

n of

1-D

FFT

"

Con

tiguo

us A

ddre

sses

"“M

”sa

mpl

es/n

ew v

ecto

r

“N” New Vectors "

Time

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! Detect and Intensity Remap

(R2 + I2) Log 10

Input IntensityO

utpu

t Int

ensi

ty

Piece-Wise Linear Remap

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Algorithm vs. Computer Architecture

! The algorithm processing requirements USUALLY define the computer– Project/Program Requirements

$ Time to solution (throughput)$ Data acquisition geometries & modes " Range of data set sizes$ Processing options in the baseline algorithm

– Derived Requirements that Define the HW Architecture$ Sustained/Peak FLOPS (floating point operations per second)$ Main memory size$ Processor to memory bandwidth$ Memory to memory bandwidth$ Disk I/O bandwidth$ Processed and Unprocessed data archive size

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Algorithm vs. Computer Architecture! Cost and Technology issues force compromises

– Can’t store the input and output data totally in main memory$ Implies a multiple-ingest approach$ Large data management implications

– Computation-bound. One CPU can’t handle the load.$ Implies parallel processing, special purpose processors, or both$ Perhaps exploit mathematical separability to improve efficiency$ Further data management implications

– I/O-bound$ Overlapped processing and I/O?$ Parallel I/O streams?$ Even greater data management implications

– Memory bandwidth-bound. Large corner turns are too slow.$ Hardware architecture implications$ Again, data management implications

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! Data management for the computer architecture is a significant algorithm complexity factor!

! I can probably architect a dedicated system for SAR ground processing, but…

! I don’t want to have different algorithms for different computerarchitectures

! Is it possible to architect an algorithm for maximum portability?– Lets explore the data management issues, then decide

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! Multiple Ingest– First scenario (brute force)

– Second (sequential) & Third (parallel) scenarios

AlgorithmFunction

1

1 2

4

6

3

5

AlgorithmFunction

2

7 8

10

12

9

11

AlgorithmFunction

3

13 14

16

18

15

17

AlgorithmFunction

1

AlgorithmFunction

2

AlgorithmFunction

1

AlgorithmFunction

2

AlgorithmFunction

1

AlgorithmFunction

2

AlgorithmFunction

3

AlgorithmFunction

3

AlgorithmFunction

3

1 2 3

5

8

4

7

6

9

10

12

14

11

13

15

1 2 3

1 2 3

1 2 3

4

4

4

5

5

5

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cr

cr

Lin-Log

DFC

Range Deskew

IPFCPF

cr

AzRipple Corr.

Polar Tap

Range Taylor Wt.

RangeComp.

AzComp.

Complex Image Tap

CTM#

Polar Reformat

DET

Deskew Phase Change

# For multiple ingest, this becomes an out-of-memory transpose.@ Global. Based upon all data.

Multiple Ingest Flow: Vector Subset Loop

Vector Subset Loop (continued) Range Subset Loop

Range Subset Loop (continued) Remap Loop

Remap @

2

6 7 9

13 14 15 19

20

FFT1

RFG2A RFG2B

FFT2

CAF

RFG4 FFT3 CTM1 FFT4

RFG6

12

8

Range Ripple Correction

cc

11 Complex Array Filter

cr

AzTaylor Wt.

18RFG5

23 Magnitude Detect

27LLELLE

OFR128

Data Format Control

Output Format

Chain 1

Chain 2 Chain 3

Chain 4

-1 +1

-1-1

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Synthetic Target Phase History Generator

Syntarg

16 WriteSubset

17 ReadSubset

25 WriteSubset

26 ReadSubset

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! Computation - Bound– Mathematical Separability

$ Some 2-D tasks are performed more efficiently as separable 1-D tasks


Range Frequency Interpolation Azimuth Frequency Interpolation


Azimuth Frequency Direction

Ran

ge F

requ

ency

Dire

ctio

n

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! I/O – Bound– Multiple options for overlapping Input, Processing, and Output

$ Sequential Buffering with Processing

$ Overlapped I/O and Processing

AlgorithmFunction

Input MemoryBuffer

OutputMemoryBuffer

AlgorithmFunction

Input MemoryBuffer A

OutputMemoryBuffer A

AlgorithmFunction

Input MemoryBuffer B

OutputMemoryBuffer B

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! Memory Bandwidth – Bound– Distributed Memory Message Passing

A A

AA

F

K

P

F

KP

F

KP

B C DE

IM

G H

LJON

B

E

IM

F

KP

JN

G H

O

DC

L

Block#

Block#

Block#

Block#

PE #PE #

PE # PE #

Start Iteration 1

Iteration 3Iteration 2

B

E

CM

JH

G N

O

DI

L

B

E

CD

GH

J N

O

MI

L

Perform a local cornerTurn on each block

Do I = 1, np-1myswap = XOR(me,I)

Send block “myswap” onPE “me” to PE “myswap”

Receive block “myswap” onPE “me” from PE “myswap”

END DO

Exchange AlgorithmExchange Algorithm

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Discussion Question

! If I want to execute mathematically the same algorithm on the Network Computers that is executed on the Production Computer….

! And if I want to minimize the number of software implementations of the algorithm for cost savings…

! Then how should I design my algorithm architecture?

Fiber OpticWide-Area Network

ProductionComputer Archive

Network Computer #1

SGI/Cray J9064-bit Word

8 ProcessorsShared Memory

Vector Processor

Network Computer #2

IBM Regatta32-bit Word

16 ProcessorsShared Memory

Network Computer #4

SGI Origin 300032-bit Word

128 ProcessorsDistributed MemoryMessage Passing

ProductDistribution

Network Computer #3

Sun Blade 200032-bit Word1 Processor

Shared Memory

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Discussion Question

! Lets consider the problem in pieces– How will I use memory efficiently if one computer has a native word

length of 64 bits and the others have a native word length of 32 bits?– What are the data management issues when the entire input and output

data will not fit into main memory?$ Consider non-square input phase history$ Remember that we are performing mixed-radix 1-D FFTs (2,3,5,7)$ What impact does implementation on a distributed-memory message-passing

architecture have on memory management?– How will we perform an out-of-core transpose on a shared memory

computer …$ If the computer has one processor?$ If the computer has multiple processors working simultaneously on different

parts of the data set (multiple ingest)?

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Conclusion

! Hopefully, you can see that creating an architecture-independent transportable algorithm is a daunting challenge.

! Hopefully, you understand that addressing this problem early can cost a lot of money, but over time could save large amounts of money in software development and maintenance.

! Solving this problem can build customer confidence that your software produces exactly the same result regardless of the computing platform.

algorithm architecture for synthetic aperture radar (sar ...kuang/lm/031014.pdf · algorithm...

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