Global Persistent SAR Sampling with the NASA-ISRO SAR (NISAR) Mission Paul Rosen, Yunjin Kim, Raj Kumar, Tapan Misra, Rakesh Bhan, V

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Global Persistent SAR Sampling with the NASA-ISRO SAR (NISAR) Mission Paul Rosen, Yunjin Kim, Raj Kumar, Tapan Misra, Rakesh Bhan, V. Raju Sagi

• Scientific Observation Requirements and Trends for SAR • NASA-ISRO Synthetic Aperture Radar (NISAR) mission overview • Are there other ways to achieve a NISAR-class SAR mission?

Area Benefit Through Regular SAR Monitoring of: Global Food Security - Soil moisture and crop growth at agricultural scale - Desertification at regional scales Freshwater Availability - Aquifer use/extent regionally - Water-body extent changes - Glaciers serving as water sources Human Health - Moisture and vegetation as proxy for disease and infestation vectors Disaster Prediction & Hazard - Regional building damage and change assessment Response after earthquakes - Earthen dams and levees prone to weakening - Volcanoes, floods, fires, landslides Climate Risks and Adaptation - Ice sheet/sea-ice dynamics; response to climate change - Coastal erosion and shoreline migration Urban Management and - Urban growth through coherent change detection Planning - Building deformation and urban subsidence Human-activity Based Climate - Deforestation’s influence on carbon flux Change - Oil and gas reservoirs

• Since SEASAT in 1978, the US science community has been looking forward to a free-flying SAR mission • It has not been for lack of trying: • Selected community recommendations: • 1994 Letter to NASA ESD recommending a free-flying SAR at L-band in 8-day repeat • 2002 SESWG Report ”InSAR everywhere all the time” • 2002 EarthScope Executive Committee recommending InSAR as the 4th pillar of EarthScope • 2004 SAR Workshop and Report recommending L-band Polarimetric SAR • 2007 Decadal Survey recommending DESDynI long-wavelength polarimetric radar • Proposals • 1994-1995 SIR-C free-flyer proposal • 1996 LightSAR commercial/science dual use L-band and X-band earmark • 1996 ESSP ECHO-1 • 1998 ESSP ECHO-2 • 2002 ESSP ECHO-3 • 2004 InSAR Satellite Concept • 2004-2007 defense/science dual use broad-band SAR • 2007-2011 DESDynI L-band SAR

jpl.nasa.gov Recommendation from 2002 Solid Earth Science Working Group Report

• Community has bold vision for continuous monitoring of Earth’s solid earth processes • Requires dense spatial and temporal sampling

Collapse of Bárdabunga Caldera (Iceland) & associated plate boundary rifting Riel et al., Geophys. J. jpl.nasa.govInt., 2015 Copyright 2017 California Institute of Technology. Government sponsorship acknowledged. NASA-ISRO SAR (NISAR) Mission http://nisar.jpl.nasa.gov

Cryosphere Solid Earth NISAR Characteristic: Would Enable:

L-band (24 cm wavelength) Low temporal decorrelation and NISAR Uniquely Captures foliagethe Earth penetration in Motion

S-band (12 cm wavelength) Sensitivity to light vegetation

SweepSAR technique with Global data collection Imaging Swath > 240 km

Polarimetry Surface characterization and (Single/Dual/Quad) biomass estimation

12-day exact repeat Rapid Sampling Applications Ecosystems 3 – 10 meters mode- Small-scale observations dependent SAR resolution Pointing control < 273 Deformation interferometry Key NISAR characteristics capture arcseconds Earth in motion: Orbit control < 500 meters Deformation interferometry > 30% observation duty cycle Complete land/ice coverage • Dense temporal and spatial sampling Left/Right pointing capability Polar coverage, north and south • Comprehensive global measurements • Targeted new science observations • Free and open data policy

Radar Antenna Instrument Subsystems: Reflector • L-Band SAR (JPL) • S-Band SAR (ISRO) • Instrument Structure (JPL) • Radar Antenna (JPL)

Radar Antenna Structure S-SAR Feed RF Aperture Boom Attach L-SAR Feed RF Point Aperture Radar Antenna L-SAR Radar Boom Instrument Controller and RF Back-End (inside)

L-SAR Digital S-SAR Signal Proc L-SAR Transmit Electronics Electronics (Inside) ISRO Spacecraft (& Receive Modules GSLV-2 launch) Instrument Structure also houses GPS unit and Solid State Recorder jpl.nasa.gov Copyright 2017 California Institute of Technology. Government sponsorship acknowledged. L-SAR Architecture State(Only Recorder Horizontal InterFace Polarizationboards (SIF), and Shown)1 Discrete Output In order to facilitate proper beam formation, the DES has Board (DOB), make up the Prime and Redundant Radar also implemented real-time closed loop calibration to allow Instrument Controller (RIC). channel-by-channel phase and amplitude correction to accommodate changes in individual transmitter and receiver 1 2 3 4 5 6 7 8 9 0 1 2 p p p 0 0 0 0 0 0 0 0 0 1 1 1

A A A Transmit

R R R responses due to variations from temperature and aging. F F F

H H H H H H H H H H H H o o o ------t t t

M M M M M M M M M M M M Receive R R R R R R R R R R R R T T T T T T T T T T T T ModulesThe collection of qFSP, SSP, SIF, and HKT are known as Down Stream Boards (DSB).

J13,J9,J26 J14,J10,J27 J15,J11,J28 J16,J12,J29 J1-1 J1-2 J1-3 J1-4 J13,J9,J26 J14,J10,J27 J15,J11,J28 J16,J12,J29 J1-1 J1-2 J1-3 J1-4 J13,J9,J26 J14,J10,J27 J15,J11,J28 J16,J12,J29 J1-1 J1-2 J1-3 J1-4 E! J19 J19 J19 A! qFSP-H0 qFSP-H1 qFSP-H2 First Stage Processors J4 J7 J5 J2 J8 J3 J6 J30 J4 J7 J5 J2 J8 J3 J6 J30 J4 J7 J5 J2 J8 J3 J6 J30

Digital Power System J14 J14 6 6 J J 7 7 l l J J

Multi-pin Connector e DOB-P SBC-P e DOB-R SBC-R

J3 J10 J7 J5 J8 J20 n n !!!!!!!!!!! ! 8 8 a a J J P P

SMA Coax Connector NVM-P NVM-R 9 9

t t Timing, J J ! n n 0 0

DSP-PCU-H o o 1 1 r r

Axon 2-way Connector J J F F

CTB-P CTB-R 1 1 B B 1 1 J J

Axon 4-way Connector T T C C 2 2 1 1

J J Telemetry, SSP-H HKT-P HKT-R D F 3 3 ! ! 1 1 J J 9 9 J SIFH-P J SIFH-R P P 2 2 F F 1 1 Solid State

Second J J H H F F

J2 J1 J15 J16 I I 3 3 S S 1 SIFV-P 1 SIFV-R J J J14 J14 Stage RICP-PCU RICR-PCU Recorder Processor Interface

Figure 1 : Block Diagram of H-polarization components of NISAR Digital Electronics Subsystem !!!!!!!!!!! ! ! jpl.nasa.gov III. HARDWARE DESCRIPTIONS B! Legend:! A!–!Quad!First!Stage!Processor!(qFSP)! A major function of the DES is on-board digital processing D!–!Control!and!Timing!Board!(CTB)! B!–!Second!Stage!Processor!(SSP)! of the radar echo signal after digitization. Figure 2 shows the E!–!Solid!State!Recorder!Interface!(SIF)! flow of the data through the DES. F!–!Housekeeping!Telemetry!Board!(HKT)! !!!!!! qFSP-H3 qFSP-V2 qFSP-H2 qFSP-V1 qFSP-V0 qFSP-H2 SSP-V RIC qFSP-H1 Control to TRMs Figure 3 : Digital Electronics Subsystem Custom Developed Hardware SSP-H qFSP-H0 Command RAD750

FPGA g Handler and n

i NVM TRM-H1 ADC Telemetry 80MHz BP x m SSP (240MSPS) r Tx-Cal s

g Aggregator o k BFPQ

Filter n F

n CTB g i i - t n Calibration L & LUT

i u

Odd m

Rx-Cal T o a m G Processor R g

r HKT

e SSP n

d BFPQ M o

B A. Quad First Stage Processor TRM-H2 ADC n

F k

80MHz BP x l Filter - a & LUT c

(240MSPS) t a

Tx-Cal a g a

t SIF-V m i P

Control n

i a m g a r To SSR r i

e BFPQ Calibration t SSP e and o D f a B

Rx-Cal F

SIF-H l & LUT D

Processor y u

Timing Filter a a r t B t

a ADC a TRM-H3 i

Handler a d D 80MHz BP g x t The qFSP interfaces with 4 independent Transmit/Receive BFPQ (240MSPS) i a Tx-Cal n

D SSP D o

s & LUT c k y

r Filter e Calibration n i a S

Rx-Cal L Processor Even T m i G TRM-H4 ADC r Modules (TRMs) to receive and digitize the RF signals from P

80MHz BP x M (240MSPS) Tx-Cal Calibration Rx-Cal Processor each TRM. The qFSP also calibrates each individual channel Command and Telemetry Including: L-Band Signal SerDes Link 80MHz Bandwidth - serial command link 1257.5 MHz Center Freq - serial telemetry readback link and provides the timing and control to the TRMs. After - discrete timing and control signals digitization the qFSP uses FIR filters [11] to digitally filter Figure 2 : DES Data Flow Block Diagram and decimate each channel and then scales the signals with a complex weighting coefficient and sums the contributing The SweepSAR technique, while theoretically elegant, channels as part of the first step in onboard digital beam brings a host of practical complications in implementation. formation. Timing and synchronization are essential aspects Primarily, the DES is required to track and process multiple of the operation of the qFSP and will be discussed in the echoes simultaneously. In the NISAR L-band instrument context of the full instrument in a dedicated subsequent implementation, four simultaneous echoes are accommodated section. to support the maximum pulse repetition frequency (PRF) of ENOB vs input power: Sine wave clock ENOB vs input power: Sine wave clock 3100 Hz while maintaining 240 km swath coverage. 60 12 Historically, radars process an individual echo within each 50 10 pulse repetition interval (PRI), but the SweepSAR paradigm 40 8 necessitates a shift to multi-threaded real time on-board 37.5 30 6 37.5 processing. 1267.5 1267.5 SNDR (dB) 20 ENOB [bits] 4 Another consequence of the SweepSAR technique is the high data rates and resources required to accomplish multi- 10 2 channel digitization, digital beamforming, and mode 0 0 -60 -50 -40 -30 -20 -10 0 -60 -50 -40 -30 -20 -10 0 dependent filtering. The digital signal processing is Input power [dBFS] Input power [dBFS] distributed in two stages to optimize resource utilization and Figure 4 : SNDR and ENOB at baseband and L-band minimize hardware complexity. The details of the signal processing at each stage will be described in the subsequent In order to directly subsample the L-band received signal sections for the quad First Stage Processor and Second Stage and still maintain sufficient signal-to-noise ratio to obtain Processor. NISAR L-band Radar Electronics

Waveform generator and Transmit-Receive Radar Computer (2) up-converter (2) Modules (24)

Radar Digitizer, Decimator and Second-stage Beamformer First-stage Beamformer (6) and Formatter (2) jpl.nasa.gov Copyright 2017 California Institute of Technology. Government sponsorship acknowledged. NISAR Swath Coverage

• All science disciplines require frequent coverage over global targets • NISAR approach would acquire sufficient swath to cover equatorial ground track extent è Global access at desired time sampling and imaging characteristics • SweepSAR technology being implemented independently by both JPL and ISRO • Transmit pulse with full feed illumination • Track echo digitally with individual receivers (12 at L-band; 24 at S-band) • Assemble individual receivers into a full- ~236 km Earth-fixed swath measurement ground track spacing at equator for 12-day repeat orbit

jpl.nasa.gov NISAR Systematic Observations L-band globally – S-band over selected areas

Repeated every 12 day cycle for the life of the mission

No target conflicts: Planned overlapping targets launch: 2021 uses union of all Colors indicate modes specified different radar modes

C. Ballard, JPL • Six-day or shorter sampling of Earth – 3 petabyte of raw data per year • Required to track dynamic changes and mitigate noise in three discipline areas • 77% chance of observing any location at US latitudes within 4 days of a disaster jpl.nasa.gov Copyright 2017 California Institute of Technology. Government sponsorship acknowledged. What about a constellation of satellites to achieve same capabilities? • Constellations of smaller, standardized satellites are being developed to lower cost and develop commercial markets

Capability NISAR Small SAR Wavelength L and S-band X through L various Repeat Pass Interferometry – < 0.1o pointing ? orbit and pointing control stability < 300 m orbit tube 12-day sampling – wide swath 240 km strip ~30 km strip Polarimetry – aperture size and SP-QP: 12 m SP-QP: ~5-10 sqm power, data rate and volume diameter aperture Resolution – data rate and 3-10 m res 3-10 m res volume ~ 1 Gbps ? Persistent Global coverage – > 50% ~10% on-orbit duty cycle jpl.nasa.gov Copyright 2017 California Institute of Technology. Government sponsorship acknowledged. Number of small SAR satellites to achieve NISAR

NISAR Swath NISAR L-band duty cycle NISAR S-band duty cycle

× . × . � = � = × ×

smallSAR Swath Small SAR duty cycle

• Under assumptions on previous page

– 40 L-band radar satellites – 8 S-band radar satellites

16 jpl.nasa.gov What about continuity beyond NISAR? Or Densification?

• NISAR represents the first step toward SESWG and continuing community recommendations – 1-day repeat – Global coverage – Finer resolution – Greater vector diversity – Multi-decade time series • Means for continuity in the age of affordability – International coordination – SmallSAT constellations (Public and private) – Rethink science requirements