quellenangabe institut für hochfrequenztechnk und...

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1Institut für Hochfrequenztechnk und RadarsystemeQue

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1Institut für Hochfrequenztechnk und Radar

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SRTM Mission CharacteristicsOrbital altitude 233,1 kmInclination 57,0 ºFlight duration 11 days, 166 revsFlight attitude (roll,pitch,yaw) 301º, 180 º, 0 º, ± 0,1 º, Total payload weight 13405 kg Total payload power/energy 7,14 kW, 9,8 kW peak/903kWhNumber of data tapes 330 equiv. 12250 GbyteCrew members G.Thiele, J.Voss,J.Kavandi, M.Mohri,

K.Kregel, D.L.P.Gorie

Launch /Mission11.-22. February 2000, 17:43 GMTOrbiter/Space ShuttleSTS 99, OV 105 Endeavour

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SRTM Within Shuttle Bay

Remote Sensing Technology Institute

M. Eineder, 30.11.2001

SRTM Space Segment

RX-only-antennas 60 m Mast

TX/RX-antennas

2 Single-Pass-Interferometers:

C-band

C-band

C-band (NASA/NIMA):

225 km swath width

⇒ full coverage (± 60° lat.)

< 10 m relative vertical accuracy

X-band

X-band

X-band (DLR/ASI):

50 km swath width

⇒ partial coverage

< 6 m relative vertical accuracy

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X-SAR/SRTM Project Organization

NIMA NASA

DLROberpfaffenhofen

Project Management

ASI

JPL

MOU MOU Letter Agreement

DLRProjectsDirector

Dornier(DSS)

Science Activities

DLR(HF-Institut)

Mission-Operations

DLR(GSOC&HF)

Calibration &Validation DLR(HF-Institut)

System-Engineering DLR(HF-Institut)

Data Processing

DLR(DFD)

Flight Instrument Development

Integration & TestSupport

ContractAMILGEO

Letter Agreement

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X-SAR/SRTM Height Error(Only X-SAR system)

Distance from nadir over swath / km

H e ig h t E rro r A s sum p tio ns (M id d le o f S w ath )R ela tive (30 seconds) A bso lute (11-days)

A ssum ed Accuracy H eigh t Error A ssum ed Accu racy H eigh t Error

B aseline Tilt A ng le Error 2 a rcsec 3 .0 m 9 a rcsec 13 .4 m

B aseline Leng th E rro r 1 .3 m m 0.8 m 4 .0 m m 2.6 m

Instrum ent Phase E rro r 4 .0 deg 4 .2 m 4 .0 deg 4 .2 m

O verall S ystem Erro r 1 .6 m 1 .6 m 1 .6 m 1 .6 m

T o ta l (R S S ) 5 .5 m 14 .4 m

X-SAR/SRTM Height Error Sources:• Instrument Phase Error• Random Phase Error• Ambiguity Phase Error• Baseline Length Error• Baseline Tilt Angle Error• Atmospheric Error• Position Error• Calibration Error• Slant Range Error• Processing Error

X-SAR/SRTM Performance

Performance Requirements:• Relative Height Accuracy (90 %) < 6 m• Absolute Height Accuracy (90 %) < 16 m

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WissenschaftExperimente

Missions-Betrieb

Kalibrierung&Validierung

RadarsystemTechnik

DatenVerarbeitung

DLRProjektleitung

Institut für Hochfrequenztechnik

GSOC undInstitut für

Hochfrequenz-technik

Institut für Hochfrequenz-

technik


technik


technik

DeutschesFernerkundungs

Datenzentrum

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Deployed 60 m SRTM mastat AEC-ABLE

Stacked mast with cables ( 3m )

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225km45kmSwath

4,9/37,5°4.9/0.25°5,3/0,28°5.5 /0.14°3 dB Beam Elevat. /Azimuth -19 dB-18 dB -21 dB-20 dBElevation Side Lobe40,0 dB42.8 dB 41,8 dB43.5 dBMain Antenna Gain 0.7m x 8m0.7 m x 12 0.4m x 6m0.4 m x12mMain Antenna Area

1.7 kW3.5 kWRadiated Peak Power60 dBTotal Dynamic Range

25 m / 13 m20 m / 10 mRge Res.10 MHz/20 MHz BW

30m25 mAzimuth Resolution (4 looks)

36.5, 46.5,53, 5836.5,46.5,53,5855.554.5Off Nadir during Mission/°

15- 55 elec.15 - 55 elec.54-55 mech.15-55mech.Adjustable Off-Nadir /Degree >25 dB39 dBPolarization Isolation

5.3 GHz HV5.3 GHz HV9.6 GHz V9.6 GHz VVFrequency, Polarization

C-Band Secondary

C-Band Primary

X-Band Secondary

X-BandPrimary

X-SAR/SRTM Radar Specifications

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X-SAR Outboard Antenna and Electronics

LNA

ϕ

LNA

ϕ

LNA

ϕ

LNA

ϕ

LNA

ϕ

LNA

ϕ

XDC Mast

Phase control

Phased Array Antenna

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X-SAR Antenna Characteristics

Elevation angle off boresight / deg Azimuth angle off boresight / deg

Rel

ativ

e in

tens

ity /

dB

Rel

ativ

e in

tens

ity /

dB

Primary Antenna: slotted waveguidearray (transmit & receive)(12 m x 0.4 m)

Secondary Antenna: phased array(6 m x 0.4 m) receive only

Elevation Two Way Pattern Azimuth Two Way Pattern


M. Eineder, 30.11.2001

X

C

photo © JPL

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SRTM Antenna AlignmentExample showing antenna misalignment effects and design to reduce the misalignment

– YOCS

(A) Bending in Y-Z Plane (Roll) (B) Bending in X-Y Plane (Yaw) (C) Twisting along Y Axis (Pitch)

Cross Track

Alo

n g Track

Near

Outboard Antenna Footprint

Inboard Antenna Footprint

Far Cross Track

Alo

ng Track

Near Far

Outboard Antenna Footprint


Cross Track

Alon

g Track

Near FarOutboard Antenna Footprint


• Impacts – Lose SNR and swath – Baseline vector change

• The Observable – AODA measurements – Radar echo profiles

• Corrective Measures – Main antenna electronic

steering in elevation

• Impacts – Lose SNR and swath – Baseline vector change

• The Observable – AODA measurements – Radar echo Doppler estimates – Radar echo profiles

• Corrective Measures – Outboard structure adjustment in

yaw – Main antenna electronic steering

in azimuth – Outboard beam tracking

• Impacts – Lose SNR and swath

• The Observable – AODA measurements – Radar echo profiles

• Corrective Measures – Outboard structure adjustment in

pitch – Main antenna electronic steering

in azimuth – Outboard beam tracking

– Y ICS

ZOCS

ZICS

XICS II XOCS

– YOCS

– Y ICS

X ICS X OCSXICS

ZIC S II ZOCS Y ICS = Y OCS

X ICS

XOCS

ZOCS ZICS

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117 tapes for X-SARrecording time 59 minutes max90 Mbit/sec datarate50 playbacks, 2 minutes each

SRTM Data Recording on board

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System Parameters of the X-SAR InstrumentHistorical development and restrictions:

• Orbit height ranging from 233 km to 249 km (coverage requirement of C-Radar)• PRF limited to eleven fixed values ranging from 1240 Hz up to 1736 Hz• Off-nadir angle higher than 51 degrees to avoid interference with the Attitude and

Orbit Determination Avionics (AODA)

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Cargo Bay Payload Layout

Star Tracker(STA )

GPS A ntenna

X-B and Outb oard Elec tronics

F ORE

AF T

C an is terOutb oard Supp ort Stru ctu re (O SS)

C -Band M ain A ntenn aL -Band M ain A ntenna

X-B and M a in A ntenn a

GPS A ntenna

Pallet A ntenn a Trun ion

A ntenna C ore Stru ctu re (A CS)

A OD A Su ppo rt Pane l (ASP)

A stros Targ et Tracker (ATT )

IR U

An ten na Tru nio n (ATS)

GPS An ten na

GPS A ntenn a

M A ST

M ilkstoo l

A ntenna C ontrol le r (CP DU )

GPS A ntenna

LED Targets (OTA )Fl ip Hinge

X-Band Outb oard An ten na

A FT Elec tro nics Panel (A EP)

GPS Receivers

A FT

X-Band 2nd Ch an nel Electron ics

Elec . D is tance M eter (ED M )

C -To -L D ow nconverte r

O utbo ard A ntenna B racketOu tboard C orner C ube

C -Band Ou tboard A ntenna

B eam A uto-Tracker

Courtesy JPL

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Payload Flight Segment Configuration

XAE: X ANTENNA ELECTRONICS XCB: X COMBINER BOX XDC: X DOWN-CONVERTER XDU: X DISTRIBUTION UNIT XOA: X OUTBOARD ANTENNA (PANELS) GPSA-2a/b: GPS ANTENNAS OTA: OPTICAL TARGET ARRAYS GPSA-2a/b: GPS ANTENNA/LNA (OUTBOARD) BAT: BEAM AUTO- TRACKER CLDC: C-TO-L DOWN-CONVERTER & CAL COA: C OUTBOARD ANTENNA COR: CAL OPTICAL RECEIVER CPDU: CNTL & PWR DIST. UNIT OAS: OUTBOARD ANTENNA SUBSYSTEM

AODA SENSOR

PANEL (ASP)

STA

IRU

ATT SA

DSCU1

DSCU2

HVE

RFE

TSS

DCE2

SIUDAE

IFD

RAE

GPSR- 1/2

CSM

CATSMDA

RIO

CTTA1

CTTA2

EXCITER1

EXCITER2

VSN

CV DRVR/RCVR

CH DRVR/RCVR

LH DRVR/RCVR

LV DRVR/RCVR

RC

BS

DCE1

NEWOLD MODC-RADAR

NEWOLD MODSMS

NEWAODA

NEWOLD MODX-RADAR

LEGEND:

PDA

MPMC

PHRR1

PHRR2

PHRR3

APC-1/2

DDRE

APC1/2: AODA PROCESSING COMPUTERS

DDRE: DIGITAL DATA ROUTING ELECTRONICS

HDDT: HIGH DENSITY DIGITAL TAPE

PHRR: PAYLOAD HIGH RATE RECORDER

RIC: RECORDER INTERFACE CONTROL

RDA: RADAR DATA ANALYZERS

DDHA1

DDHA2

DDHA3

DDHA4

LVE

C/AI: CAL/ANTENNA INTERFACE COT: CAL OPTICAL TRANSMITTER DDHA1-4: DIGITAL DATA HANDLING ASSEMBLY RFES: RF ELECTRONICS SUBSYSTEM RCBS: REDUNDANCY, CAL & BITE SELECT VSN: VIDEO STEERING NETWORK

CTTA: CNTL, TMG AND TLM ASSEMBLY DSCU: DEPLOY/STOW CONTROL UNIT MPMC: MAST POWER AND MOTOR CONTROL PDA: POWER DISTRIBUTION ASSEMBLY RIO: REDUNDANT I/O HVE: HIGH VOLTAGE ELECTRONICS LVE: LOW VOLTAGE ELECTRONICS DCE1/2: X DATA & CONTROL ELECTRONICS RFE: X RADIO FREQUENCY ELECTRONICS

X-ELEC. PLATE

DSCU PLATE

PDA PLATE

CTTA PLATE

DDHA PLATE

RFES PLATE

AFT ELECTRONICS PANEL (AEP)

CAN

MILK STOOL

YA

PAFA

FLIP HINGE

MAST

XBS

XTSTR

IDR

IVE

ACS/ATS

GPSA- 1a

GPSA- 1b

XMA

LMA

CM

A

CARGO BAYAFT DECK PALLET SMS

PALLET SMSCARGO BAYAFT DECK

CMA: C MAIN ANTENNA LMA: L MAIN ANTENNA GPSA-1a/b: GPS ANTENNAS ACS: ANT. CORE STRUCTURE ATS: ANT. TRUNION STRUCTURE CAT: CANT. ATTACHMENT TRUSS CAN: CANISTER CSM: CONNECTOR SEPARATION

MECHANSIM FA: FLIP ACTUATOR LPS: LAUNCH PIN STRUCTURE PA: PITCH ACTUATOR PICA: PYROTECHNIC INITIATOR

CONTROL ASSEBLY SMDA: SUBSTITUTE MOTOR DRIVE

ASSEMBLY TSS: TRUSS SUPP. STRUCTURE YA: YAW ACTUATOR XBS: X-ANT. BACK STRUCTURE XTS: X-ANT. TRUNION STRUCTURE XMA: X PRIMARY ANTENNA

NOTE: PLACEMENT OF HARDWARE PIECES IN THIS DWG MAY NOT CORRESPOND TO FLIGHT CONFIGURATION

APC1 APC2

RIC

RDA3

RDA1

RDA2

NOT SHOWN: PHRR SPARES AND APC/RIC/RDA SPARES; ALSO HDDTs > 264.

EDM 1-4

ATT EA

PSU

XOA

OTA

XCB

XDC

XAECLDC

GPSA- 2b

GPSA- 2a

OUTBOARD SUPPORT

STRUCTURE(OSS)

CO

AP

BAT

XDU

LPS

C/A

I; CO

T

COR

OAS

CPDU

COA

DAE: DIGITAL ADAPTER ELECTRONICS IFD: INTERMEDIATE FREQ & DEMODULATION UNIT PSU: POWER SUPPLY UNIT RAE: RF ADAPTER ELECTRONICS ATT SA: ASTROS TARGET TRACKER SENSOR ASSEMBLY ATT EA: ATT ELECTRONICS ASSEMBLY GPSR-1/2: GPS RECEIVERS EDM: ELECTRONICS DISTANCE METER IRU: INERTIAL REFERENCE UNIT SIU: SENSOR INTERFACE UNIT STA: STAR TRACKER ASSEMBLY

PICA

COLD-GAS TANKS

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PRF Selection / Timing

Fixed PRF:

1674 Hz

Pulse bandwidth: 9.5 MHz

Down link data rate: 45 Mbit/s

Pulse length: 40 µs

Quantization: 8 bits/sample

Echo sampling frequency: 11.25 MHz

PRF-Restrictions

PRF / Hz

Offn

adir

ang l

e /

deg

Timing at Equator Timing at +/- 57 deg latitude

Time relative to start of transmit pulse / microsecTime relative to start of transmit pulse / microsec

Data Window

Antenna Boresight

Nadir Return

Transmit Pulse

Echo Profile

Data Window

Antenna Boresight

Nadir Return

Transmit Pulse

Echo Profile

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Instrument Performance Characteristics

Signal-to-Noise Ratio

Transmit peak power:3300 W

Noise figure: 5.25 dB Noise figure: 2.52 dB

σ : SRL1 / SRL20

SNRadc

SNRimg

SNRadc_out

SNRvid

Distance from nadir / km

SN

R /

dB

Primary System

SNRadc

SNRimg

SNRadc_out

SNRvid


SN

R /

dB

Secondary System

RASR

Total ASR


Amb

to s

ig/

dB

Primary System

CrosstermASR

AASR

Secondary System

RASR

Total ASR

Distance from nadir / kmAm

bto

sig

/ dB

CrosstermASR

AASR

Ambiguities

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Telemetry System

Mission PlanningSystem

Command System

Performance EstimatorSystem (PE)

Radar Data Analysis

Performance AnalysisSystem (PA)

>12 hours before DT

> 6 hours before DT

during DT

during / after DT

Mission Planning and Operations System•Data Take start and stop times•Selection of radar parameters•Downlink and play back times•Tape management

•Check parameter selection•optimize gain setting

•Generate command sequence•Uplink onboard sequencer load•Real-time commanding

•Monitor instrument health•Monitor instrument function

•Monitor DT performance (echo profile)•Monitor parameter settings

•High rate data analysis (bit error rate)•Antenna alignment (Doppler centroids)•Quick-look radar image processing•Quick-look interferometry

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C/X Joint Operations Agreement1. Priorities C-band DEM, X-band DEM

2. PHRR Operations PHRR 3 =X, X reassign to CA or CB, PHRR4- Xreplace with spare,

3. DDRE Contingency activate bypass,

4. High-Rate Live Downlink whenever possible, channels sequentially by DT

5. High Rate Playback 2 minutes of last DT, ratio C:X=2:1, contingencies

6. Command Uplink AODA, real-time, sequencer loads

7. Datatake Planning joint C,X DT’s same start/stop, no short-term plan

8. Antenna Tilt X-antenna tilt < 0 deg, Tilt CMD by C- Control

9. Beam Adaptive Tracker use decided by C-Radar

10. Milkstool (beam alignment) optimize C and X alignment

11. Energy Contingency shortage shared

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X-SAR Operational Constraints3: The Orbiter attitude should be constrained so that the sun does not shine on the radiating surfaces of the SIR-C/X-SAR antennas. If the Orbiter must maneuver to an attitude that violates this constraint, antenna surface temperatures shall not exceed: (1) +40 deg C (inboard and outboard, antennas non-operating) or (2) +30 deg C (inboard and outboard, antennas operating);

7:X-SAR tri-drive operations. For loss of one motor drive system, nominal experiment ops may continue. For loss of two motor drive systems, use of the remaining motor system will be minimized. EVA capability exists to stow antenna if the third motor system fails.

16:Power up of X-SAR outboard heater electronics (PSU) when temperature is below –30 deg C. If external environmental temperatures near the X-SAR outboard electronics (XOE) are below -30 deg C,the PSU shall not be powered-on by the crew (SSP/S9). The Orbiter shall maneuver to warm the XOE toabove -30 deg C so that switch-on may occur.

17: Potential damage to X-SAR outboard electronics (XOE) boxes if external environmental temperaturesexceed -40 deg C when the PSU is unpowered (SSP1/S9). If external environmental temperaturesexceed -30 deg C when PSU is unpowered, the Orbiter will maneuver to a warmer attitude. Prevent permanent damage to the X-SAR outboard electronics.

20:The X-SAR antennas should not be allowed to get colder than -117 deg C. If X-SAR antenna temperatures drop below -112° C, maneuver the Orbiter to a warmer attitude.The X-SAR antennas have been qualified from -150 deg C to 70 deg C (non-operating). The X-SAR components that are the limiting factors are the radiating waveguides and the reinforcement frame. However, the manufacturer recommends not exceeding -117 deg C to +40 deg C to avoid degradation of antenna performance.

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Specific X-SAR Crew Activities (crew procedures)

• X-SAR activationMain antenna deploy

• PHRR 3, Tape changes

• X-SAR deactivationMain antenna stow

Nominal Operations Non nominal Operations POCC support

X-Ops

C-InstrumentAMS

X-OpsX-Ops

C-InstrumentAMS

• X-SAR B CMD Swap source PSP1(2) to 2(1)•Tilt angle Display Lookup Table

• Tilt Mode Sel Man• Antenna OVD Ply (ANT POS)• Tilt 3(4)ENA• ANT POS(ANT S TO)tb-LAT(gray)• ANT HTR 1(2,3),tb- bp

• No confirm PSU Power On• No PSU Power On• No confirm PSU Power Off• No PSU Power Off

• EVA-Restow X-SAR Antenna

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X-SAR/SRTM Data Flow

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X-SAR Calibration

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X-SAR/SRTM Error Budget

Performance Requirements

• Relative Height Accuracy(90 %) <6 m

• Absolute Height Accuracy(90 %) <16 m

X-SAR/SRTM Height Error Sources

•Baseline Tilt Angle

•Baseline Length

Instrument Phase

•Random Phase

Ambiguity Phase

• Atmosphere

• Position

• Calibration

• Slant Range

• Processing

14,4 m5,5 mTotal4,2 m4,o deg4,2 m4,0 degInstrument Phase2,6 m4,0 mm0,8 m1,3 mmBaseline Length13,4 m9 arcsec3,0 m2 arcsecBaseline Tilt AngleErrorAccuracyErrorAccuracyError Type

Absolute (11 Days)Relative (30 seconds)Height Error Examples (Middle of Swath)

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Calibration Concept

Ocean Sea Level

Calibration

• Estimation of systematic errors• Monitoring of system parameters and instrument performance• Characterization of instrument parameters• Development of calibration models (parameter drifts as a function of time and temperature )

• Ocean as reference height (sea surface height model)Known orbit with respect to WGS 84 ellipsoid

Ground Control

PointOcean Sea

Level Calibration

Measured height

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X-SAR/SRTM Calibration Phases

• Preflight concept definition phase including sensor characterization, calibration algorithm development and implementation

• Ground campaigns during the mission

• 6 months commissioning phase: generation of static and dynamic calibration files, analysis and modeling of parameter drifts with temperature and time

• Operational calibration and validation

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Required data for X-SAR calibration/validation

DLR/User

ERS-1altimeter data

TOPEX-POSIDON data

AODA

MPOS

X-SAR

DLR/User

X-SAR

DLR/User

DLR/User

GCP data base

High precision DEMs

Tide tables

Geoid undulations

AODA-PADR file

X-SAR HK data

Ocean datatakes

Calibration test sites (CRs)

Cal tone

Maps

GDPS X-GDPS

NIMA/JPL

DLR/User

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AODA System OverviewInstruments Function Accuracy Rate

X Y ZGPS2 GPSR &4 GPSA

C-band area centroids (ACS and OCS) state vectors - Position (WGS 84) - Velocity (WGS 84)Time tag

1m0.05m/s

1m0.05m/s

1m0.05m/s 1 Hz

Star TrackerAssembly (STA)

Estimates inertial attitude of ICSSTA boresight orientation wrt inertial space

InertialReferenceUnit (IRU)

Propagation of inertial attitudes between STA updates

roll5.0

0.05arcsec

pitch36.0

0.05arsec

yaw 5.0

0.0.5arcsec

1 Hz

ASTROS (ATT)& Optical TargetAssembly (OTA)

Estimates the relative attitude and position of the OSS ->C-InSAR baseline and support antenna alignmentTracks 3 LED targets at 60 m distance

0.8arcsec

- 0.8arcsec

4 Hz

ElectronicDistance Meter(EDM)

Distance measurement to OCS and X-SAR backstructure- 2 for ICS to OCS vector length determination (red.)- 2 for ICS to inboard X-SAR area centroid Y & Z offsetdetermination

- 0.5mm

0.5 mm -0.5mm

0.5Hz

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AODA Flight System Functional Diagram

APC 28VDC Cabin Pwr

serial digital i/o

MET/SIO sync

MET/SIO clk

X-OSTT

serial digital data

power

serial digital i/oanalog data

power

pulse trains & clocks

analog datapower

serial digital i/opower

OTA(3 arrays)GPSA-2

GPSA-1

ATTEA

IRU

STA

PCB128VDC

Main Pwr

serial digital dataPDI

pwr/rf

downlink

power

LNA

LNA

SIU

AMTC: Auto Mast Twist CompensationAPC: AODA Processing Computer (Thinkpad)ATT: ASTROS Target TrackerDAE: Digital Adapter ElectronicsEA: Electronics Assembly (ATT)EDM: Electronic Distance MeterGPSA-1: GPS Antennae Set 1 (inboard)GPSA-2: GPS Antennae Set 2 (outboard)GPSR: GPS ReceiverIRU: Inertial Reference UnitLNA: Low Noise AmplifierMET: Mission Elapsed TimeMPMC: Mast Power & Motor ControlOSTT: One Second Time-TickOTA: Optical Target AssemblyPCB: Power Control BoxPDI: Payload Data InterleaverSA: Sensor Assembly (ATT)SIO: Serial Input/Output (shuttle att/sv data)SIU: Sensor Interface UnitSTA: Star Tracker Assembly

Payload Bay and Outboard Support Structure Crew Cabin

C-RADARMPMC

discrete (bi-level) i/o

discrete (bi-level) i/o

GPSR-1

GPSR-2

LNA

MET/SIO data

X-RADAR DAE

OPS RCRD

serial digital i/o (x4)

power (x4)EDM(x4)

ATTSA

ctrl/data

MET/SIO sync

serial digital data

powerMET/SIO sync

AMTC discrete

output signals

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SRTM Baseline Measurement Breakdown

Example showing how the baseline measurement is broken down into respective subsystems

GPS Antenna 1

GPS Antenna 2

Inboard C-Band Phase Center

Inboard Coordinate System Origin

Outboard Coordinate System Origin

A

P i

G 2

Outboard C-Band Phase Center

B

Po

To Origin of WGS84

P

Inboard Area Centroid

Eo

E i

B = (

)

-A P i P o )

= (P -WGSGPSxP

WGSicsM ICS

ocsM+

ICSocsMWGS

icsM A- Pi+G x

- E i ( Eo+

Ei+

To Origin of WGS84

AODA

GDPS

SMS

C-RADAR

Measurement Responsibility

GPS2PWhere :

= ICS to OCS Origin VectorA

ICSocsM WGS

icsM, = Rotation Matrices to convert between Coordinate Systems

= Location of Antenna Area Centroids,P i Po

= Offset Vectors between Area Centroids and the True Phase Center of Antennas

,E i Eo

G x = Location of the x th GPS Antenna ICS/OCS

B

P = Phase Center Position Vector= Interferometric Baseline Vector

= Location of the x th GPS antenna in WGS84GPSxP

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INSTRUMENT CALIBRATION

Interferometric phase:

( )( )

(CT1attCTtestcpRAEtestcp1ant

,LNAXCBi,switchi,LNAant

outboom

i,2CT1CT

21int

615.36

61

−−−−

−−

−

Φ+Φ−Φ−Φ+

Φ−Φ−Φ−

Φ+

Φ−Φ+

Φ−Φ−=Φ

∑

∑

• caltone estimation

• phase variation of 263MHz signal on boom cablefrom phase detector

correction terms from preflight instrumentcharacterization

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Correction and Calibration of the X-SAR Data

Antenna 2LNA's

XCB

XDC

RFE

RAE

IFD

Antenna 1

Boom

135MHz

1052MHz

263MHz

WG

Secondary Channel Primary Channel

STALO

Critical Parts of the X-SAR Radar electronics

• Phase variation of radar receive signalin the six individual paths: antenna panel to XCB including LNA’sand phase shifters

• Down-conversion using 263 MHz signalgenerated in the RFE (1052 MHz) and distributedover the mast to XDC, ± 4 deg phase variationat 263 MHz multiplied by 36 in down-conversion

•Phase variation of radar receive signal running at 135 MHz over the mast cable: ± 2deg over a temperature range between -10oC and -50oC

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test coupler

Antenna

Panel #1

263 MHz

Channel 1

switch box

RX-Gain

XCB

XDC

IFD

RAE

Boom

RX-Gain

Channel 2

RFE

WG

1052MHz

cal-tonegenerator

cal-tonegenerator

downconversion

downconv.

LNA

I/Q I/Q90 MHz

RADAR RECEIVE SIGNALS

ΔΦ

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D1-D18 1.5 m Corner reflectors GermanyD19-D24 3m Corner reflectorsD25-D27 RU1-Russia-Kitab-1 RU2-Russia-Zelenchukskaya-2RU3-Russia-Zvenigorod-3RU4-Russia-Irkutsk-4RU5-Russia-Bear_Lakes-5CH1-5 Switzerland-1-5SA1-2 South-Africa-1-2 NO1-2 Norway-1-2 EG1-3 Aegypten-1-3 BK1-6 Baikal-1-6KG1-Kirgisien-1-4 IS1-2 MIRBATS-ISRAELIS3-673-HILL-ISRAELIS4-MITSPE-ZOHAR-ISRAELIS5-HIDDEN-HILL-ISRAELIS6-SEDE-ZIN/minhat-north-ISRA IS7-SEDE-ZIN/minhat-south-ISRA IS8-BEER-SHEVA/goral-ISRAELIS9-BEER-SHEVA/hatserim-ISRAEL

X-SAR/SRTM Calibration Sites


M. Eineder, 30.11.2001

DT 146.190

SRTM Calibration: Uses Ocean Data Takes

As reference surface, instantaneous ocean heights including gravity, tides,barometric pressure are used. Precision is in centimeter range.Ocean data are provided by Geoforschungszentrum Potsdam (GFZ).

Institut für Hochfrequenztechnik und Radarsysteme 9

•Data take start and stop•window position•gain selection

Downlink/Playback

TDRSS coverage

XSAR/SRTM Mission Planning

Tape management


M. Eineder, 30.11.2001

8500 kmRelative Accuracy 6 m (84%)

Absolute Accuracy 16 m (99%)

Result: Long Time Stability on DT 146.190

Azimuth cut of DEM error over a long ocean data take. Absolute accuracy requirement (16m, 90%) is easily met, the relative requirement (6 m, 90%) only after reduction of thermalnoise.

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Ocean Calibration

• Height error:

truthgroundmeas hhh −−=δ

• Error contributions from baseline length/tilt, phase and orbit height offsets

[ ]⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

δΦδ

δαδ

δδδδ=δ Φα

H

b

h H,h,h,hb,h

• MAP estimation based on prior information provided by AODAproblem sufficient SNR at 55deg incidence angle ?

Two iterations to determine static and dynamic calibration file

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SRTM Calibration:measured Height over Ocean

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Geometric Calibration

• Differential range delays from data itself by cross correlationof the speckle patterns between the two interferometric channels

• Common range delay, time tag/velocity biases using cornerreflectors, calibration sites: Oberpfaffenhofen, Mojave Desert, Australia

• Baseline length/tilt, orbit, phase offsets: estimation from short ocean data takes before/after ocean-land crossing or from GCP’s

• Residual phase errors (e.g. multipath) and system stability: long oceandata takes at the beginning and end of the mission

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SRTM Data Products

DTED (Digital Terrain Elevation Data) ⇒ ITED (Interferometric Terrain Elevation Data)

• 1 degree x 1 degree cell; origin in SW corner• elevations in meter• intervals in Arc Seconds (DTED 1: posts every 3 arcsec, DTED 2: 1 arcsec)• datum: vertical = mean sea level, horizontal = WGS 84• Specification ITED level 2

C-Band X-Bandhorizontal absolute accuracy < 20 m < 20 m ( 90% circular error WGS)vertical absolute accuracy < 16 m < 16 m ( 90% linear error WGS)

horizontal relative accuracy < 15 m <15 m ( 90% circular error WGS)vertical relative accuracy < 10 m < 6 m ( 90% linear error WGS)

HEP (Hight Error Map) ⇒TPDSlope Map ⇒ TBD

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X-SAR/SRTM Swaths over Bavaria (Calibration site)

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SIR-C Results


M. Eineder, 30.11.2001

SRTM-Fact Sheet• Orbit height: 233 km

• Mission duration: 11 days

• Cost:US Mission: $ 142MShuttle Start: $ 50 MX-SAR: $ 40 M

• Data amount: ca.10 TBytes (15000 CD-ROMs)

• 756 data takes, mapped surface: 120 x 106 km2

Areas of X-SAR Application• 115 Principal investigators

(AO)

• 1,000+ requests during andafter the mission

• Accuracy: horizontal 20m / vertical 6m (15m absolute)

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Geometric Stability

excellent baseline stability:

4 ηinc=54.50 average +-0.20

4 data from shuttle nav. system

excellent antenna co-alignment:

4 Doppler differences ca. 50 Hz between both channels

small, coupled oscillations of shuttle and boom, will be compensated

44.55

44.60

44.65

0 5 10 15 20time [s]

0.10

0.14

0.18

0.22

0.26

0 5 10 15 20

time [s]44.70

Boom tip [m]

Shuttle attitude [deg]Boom tip

Shuttle roll attitude

Eineder, M. 2000

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Results (II)

SRTM/X-SAR color coded interferogram of the peninsula of Hokkaido/Japan, MET 5/07:55:00

Eineder, M. 2000

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Throughput

11 day mission

4 69 data takes have been received and analyzed during mission

4 72 Gigabytes of data

4 99 interferograms generated

4 45 DEMs

InSAR processing of a 45 km x 170 km takes 1 hour

4 some variation depending on the phase unwrapping difficulty

4 including automated tie pointing.

processing is done on a 12 CPU SUN E4000

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Receive Signal Phase - Corrections

Antenna 2LNA's

XCB

XDC

RFE

RAE

IFD

Antenna 1

Boom

135MHz

1052MHz

263MHz

WG

Secondary Channel Primary Channel

STALO

1. No beam steering was done during mission -> No correction necessary

5. Due to major temperature variation of XDC there were high phase errors in the receive path-> Phase correction with Cal Tone (max. expected error?)6. Due to temperature variations of the mast cable there were phase errors in the receive path-> Phase correction with Mast Phase HK (max. 9°)(max. expected error for receive signal 330° within a orbit )

3. Cal Tone was in ‘cycling mode’-> Each Cal Tone path has a different Cal Tone Offset (max. expected difference 360°)4. Cal Tone Level was following IFD gain (XDC/RAE Cal Tone Att.)-> Correction of the phase jumps for different XDC/RAE Cal Tone Att. Settings with Cal Tone Att. Characterization data. (max. expected phase jump 60°)

2. Variation of XOA coax cable temperature 5°C/orbit -> Phase correction with Cal Tone ( max. expected error 0.2°)

7. Different gain settings (70 dB … 80 dB) was used-> Correction of the phase jumps for different Gain Att. Settings with Gain Att. characterization data.

(max. expected phase jump 60°)8. Due to a low temperature variation (about 2°C) of the shuttle cold plates there were minor phase errors in the receive path (RAE, IFD,RFE)-> Phase correction with Cal Tone ( max. expected error ?)

9. Low temp. variation for Coax Cable with Ref. Signal -> No Correction possible (max. expected error < 0.1°/10 min, for 1052 MHz)

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Interferometric Performance

Coherence

4 desert regions no problems so far

4 water surfaces sometimes decorrelate under calm wind conditions

Coregistration

4 currently better than 0.05 pixelShadow / Layover

4 layover no problem: < 0.06 % in alpine regions

4 shadow problems in alpine regions: ca. 7% of ground surface


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SRTM Calibration:measured Height over Ocean


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Mast Phase and Mast Temperature

-30

-20

-10

0

10

20

30

05. 22:00:00 05. 23:00:00 06. 00:00:00 06. 01:00:00 06. 02:00:00

MET

Tem

p 'M

ast_

58D

'

184,00

186,00

188,00

190,00

192,00

Mas

t Pha

se

at 2

63 M

Hz

Mast_58DMast Phase


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Mast motion and antenna alignment

1.4 0.7 0 0.7 1.4

Dynamic mast torsion (pitch axis)= max 0.05º

Dynamic mast deflection (yaw axis)= max 0.02º

Dynamic mast deflection (roll axis)= max 0.1º

0 10 20 30 40 sec

+0,04

0,00

-0,04


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Geometric Stability

excellent baseline stability:

4 ηinc=54.50 average +-0.20

4 data from shuttle nav. system

excellent antenna co-alignment:

4 Doppler differences ca. 50 Hz between both channels

small, coupled oscillations of shuttle and boom, will be compensated

44.55

44.60

44.65

0 5 10 15 20time [s]

0.10

0.14

0.18

0.22

0.26

0 5 10 15 20

time [s]44.70

Boom tip [m]

Shuttle attitude [deg]Boom tip

Shuttle roll attitude

Eineder, M. 2000Remote Sensing Technology Institute


M. Eineder, 30.11.2001

SRTM Calibration: Mast Oscillation Problem

ca. 160 km

44.60

44. 50

44.40

44.30

shut

tle ro

ll an

gle

0 1400 2800 4200 [Km]

44.20

1. Gravitygradient rotatesinterferometer

to uprightposition

2. At dead band limitshuttle fires thrusters to

return to nominalattitude

3. Shuttleaccelerationcauses mast

oscillations ...

300 meterheight

oscillations!

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Results (I)

SRTM/X-SAR Radar amplitude image of the peninsula of Hokkaido/Japan, MET 5/07:55:00


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Results (III)

SRTM/X-SAR coherence map of the peninsula of Hokkaido/Japan, MET 5/07:55:00


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Results (IV)

SRTM/X-SAR DEM of volcano Komaga-take on Hokkaido/Japan, MET 5/07:55:00


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Phase unwrapping: Komaga-take (1131m)

Moderate topography: Minimum cost flow (MCF) method gives excellent results!


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