MO4.L09 - DIGITAL BEAMFORMING SAR (DBSAR) FOR BIOMASS ESTIMATION

Goddard Space Flight Center

July 26, 2010

July 26, 2010

Digital Beamforming Synthetic Aperture RadarFor Biomass Estimation

Rafael F. Rincon, Guoqing Sun, Temilola Fatoyinbo, Jon Ranson and Paul Montesano NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA

[email protected]: (301) 614-5725. Fax: (301) 286-1810

mailto:[email protected]

Goddard Space Flight CenterOutline

• Motivation and Science Objectives

• The DBSAR Concept • System Architecture

• Operational Modes

• Biomass Retrieval Efforts

• Concluding Remarks

Goddard Space Flight CenterMotivation and Science Objectives

• Climate change constitutes one of the greatest environmental problems of this century. Quantifying the carbon cycle is one of the most important elements in understanding climate change and its consequences.

• The amount of carbon in above ground vegetation, especially forests, is poorly understood because of the difficulty in acquiring sufficient on-ground measurements of biomass across the diversity of vegetated ecosystems.

• Improved remote sensing measurement methodologies are required to understand the relationships between the biosphere and atmosphere with respect to greenhouse gases and close the current deficiencies in modeling the Earth’s carbon budget.

Goddard Space Flight CenterThe DBSAR Concept

• DBSAR is an L-band airborne imaging radar system developed at the NASA Goddard Space Flight Center (GSFC) in order to formulate, implement and test new radar techniques in support of Earth Science and planetary applications.

• DBSAR combines digital beamforming, reconfigurable waveform generation, and real-time processing in order to enable multi-mode radar techniques not possible with conventional SARs.

• DBSAR's highly innovative architecture provide the means to implement and demonstrate advanced SAR techniques that can provide the needed data for biomass studies.

• Work is currently underway at GSFC to implement robust SAR image formation algorithms for the processing of the DBSAR data in order to retrieve key biomass parameters


System Architecture• 8 channels enable cross-track scanning over a wide range of angles

• Transmit modules feature digital phase steering and amplitude taper

• Phased array antenna has 64 active microstrip patch elements

• DBSAR was designed for operation on board of the NASA P3 aircraft

Antenna

T/R

A/D

T/R

A/D

T/R

A/D

T/R

A/D

T/R

A/D

T/R

A/D

T/R

A/D A/D

T/R

Waveform Generator /

Digital Beamformer

REU

Processor

Goddard Space Flight CenterThe Real-time Processor

• Fully Reconfigurable

• Custom design

• Three Stratix II FPGAs

• Eight A/D converters

• Six SRAMs

• ARM microcontroller

• 1-Gb Ethernet interface

• Size (cm): 17 x 24 x 4

• Power: 94 W maxMixed signal board Digital signal board

System Architecture

Goddard Space Flight CenterSystem Architecture

Main Parameters

Type Microstrip Patch

Number of Patches 80

Bandwidth 20 MHz

Polarization HH, VV, VH

3 dB Beamwidth 12 Degrees

Two-Way Side Lobes < – 26 dB

Antenna Gain 21 dB

Dimensions (m) 1.2 x 1 x 0.5

Power Draw (W) 350

Weight (kg) 106

M ISC

Frequency 1.26 GHz

Maximum Bandwidth 20 MHz

PRF 40 Hz - 10 KHz

Pulse Width 1 – 100 s

Number of Transmitters 8

Output Power 16 W

Accuracy < 0.7 dB

Beam Steering Angles > 50 degrees

ANTENNA

DBSAR Calibration in Anechoic Chamber

RADAR


• Performs 1-Dimensional scanning (across track in nominal configuration).

• Capable of sequential polarimetric operation (HH,VV,VH). (New)• Employs software defined radar functions: waveform, T/R taper, digital

In-phase and quadrature (I&Q) generation, digital filtering, etc…• Implements real-time onboard processing.• Supports In-phase and quadrature (I&Q) high data rate acquisition

mode.• Capable of adjustable transmitter illumination from narrow-beamwidth

(high-gain) beam steering to wide-beamwidth illumination.• Capable of in-flight reconfigurable waveform generation • Employs noise source and closed loop calibration schemes • Uses real-time data monitoring through a customized graphical

interface unit.

System Architecture Main Features Summary

Goddard Space Flight CenterDBSAR Operational Modes

• Current operational modes include scatterometry over multiple antenna beams, several modes of Syntehtic Apeture Radar (SAR), and Altimetry.

Swath 5

Flight Path

Swath 6

Swath 4

Antenna

Swath 2

Swath 3

Swath 1

θ3θ2

θ1

θ4θN+1

θN

h

Swath 2

Flight Path

Swath 3

rx

Swath 1

rx

ry

rx

ry

ry

θ1

θ2

θ3

Total Sawth

Antenna

h

Flight Path

Antenna

Scatterometry up to 32 beams

SAR single swath / Narrow beam

Altimetry

Swath 3

Flight Path

Swath 4

rx

rx

ry

ry

θ3θ4

Total Sawth Left

Antenna

Swath 2

Swath 1

rx

ry

rx

ry

Total Sawth Right

θ2θ1

SAR Wide swath

Two sides of the track

h

Swath

Flight Path

rx

ry

θ1

Antenna

ScanSAR


DBSAR First Airborne Campaign 2008• 7 Flights where conducted on the NASA P3 aircraft during October 2008 over areas

of the Delmarva Peninsula, Eastern Shore, USA.

DBSAR Integrated to P3 aircraft

DBSAR and NASA P3 Aircraft Wallops Island, VA

Delmarva Peninsula, Eastern USA

Wallops Flight Facility

Atlantic Ocean


• A broad beam is generated by energizing a small section of the antenna

• The beam illuminates entire field of view

TX Swath

Flight Path

Antenna

DBSAR Operational ModesTx wide beam

Recv multiple narrow beams


• A broad beam is generated by energizing a small section of the antenna

• The beam illuminates entire field of view

• Signal returns are collected with the full aperture

• Several beams are synthesized simultaneously

• SAR processing is performed on each beam

Swath 3

Flight Path

Swath 4

rx

rx

ry

ry

θ3θ4

Total Sawth Left

Antenna

Swath 2

Swath 1

rx

ry

rx

ry

Total Sawth Right

θ2θ1




FLIGHT TRACK

Range Res. = 7.5 mAzim Res. = 0.5 m (single look)NESZ ≤ -28 dB (single look)

Aircraft Altitude = 4 kmAircraft Speed = 150 m/s

Image resampled and multi-looked to 10 m x 10 m pixels.




• A single beam is generated by electronic steering

• The beam illuminates a single swath

• Signal returns are collected with the full aperture

• Selected beam is synthesized on receive

• SAR processing is performed on selected beam

h

Swath

Flight Path

rx

ry

θ1

Antenna

DBSAR Operational ModesTx narrow (focused) beam

Recv narrow beam

Goddard Space Flight CenterDBSARStrip Mode

Range Res. = 7.5 mAzim Res. = 0.5 m (single look)NESZ ≤ -35 dB (single look)Image resampled and multi-looked to 10 m x 10 m pixels.

Cosine taper on TX and Rcv

Aircraft Altitude = 4 kmAircraft Speed = 150 m/s


Biomass Retrieval Efforts

• Evaluation of DBSAR and PALSAR Images over the Delmarva Peninsula.

• Biomass Field measurements over DBSAR mapped areas.

• Correlation between DBSAR backscatter and ground truth biomass.


Image calibration and evaluation using PALSAR

DBSAR

PALSAR

Biomass Retrieval Efforts

Goddard Space Flight CenterBiomass Retrieval Efforts

Wallops Biomass Field Campaign


• Coastal plain mixed forest (loblolly pine, hardwood spp.)

• Mature forest• Understory varied:

– shrub – regeneration– open

• 10 m circular plots• dGPS location of plot center• Trees > 10cm DBH: DBH,

species collected

Biomass Retrieval EffortsWallops Biomass Field Campaign

Goddard Space Flight CenterBiomass Retrieval Efforts

Wallops Biomass Field Campaign


Concluding Remarks• The biomass retrievals currently underway at GSFC using

DBSAR data will seek to generate required data to better understand radar backscatter from forests.

• Results from the DBBSAR first campaign indicated a successful performance of the radar system and its potential benefits for biomass studies.

• DBSAR was recently upgraded with polarimetric operation (HH,VV,VH) which enhances the science capability of the system.

• DBSAR’s next flight campaign is schedule in the summer 2011 when the system will be used to map forests over the US east coast.

• New techniques to be explored with DBSAR for Biomass include interferomery.


Backup Slides


Waveform Generator

• Waveform generator is fully reconfigurable .

• Transmit channels include programmable attenuators and phase shifter.

• Receive channels amplify and condition and signal returns .

• Performs internal calibration by sampling 1) the transmit signal and 2) the signal from a noise source.

System Architecture

Single Channel

Rafael RIncon

The L-Band Imaging Scatterometer (LIS) is a 1.26 GHz airborne radar recently developed at NASA Goddard Space Flight Center for flight operation onboard the P-3 aircraft. The system combines electronic beam steering and digital beamforming allowing the implementation of different scanning techniques. The LIS efforts are part of the RadSTAR initiative intended to develop the technology that enables combined radar/radiometer systems that jointly uses a single, dual frequency antenna with cross-track scanning capabilities. The new technology will enable single aperture measurements of important Earth Science Enterprise climate applications such as ocean salinity, soil moisture, sea ice, and surface water among others.


Chirp Signal Generator

Chirp Spectrum

Rack mount Host computerReconfigurable Algorithms

LIS in Anechoic Chamber

DBSAR Processor Graphical User Interface

End of PresentationEnd of Presentation


β 0 β1

Hardwood Aspen/alder/cottonwood/willow -2.2094 2.3867Soft maple/birch -1.9123 2.3651

Mixed Mixed hardwood -2.48 2.4835Hard maple/oak/hickory/beech -2.0127 2.4342

Softwood Cedar/larch -2.0336 2.2592Douglas-fir -2.2304 2.4435True fir/hemlock -2.5384 2.4814Pine -2.5356 2.4349Spruce -2.0773 2.3323

Woodland Juniper/oak/mesquite -0.7152 1.7029

Biomass equation: bm = Exp(β 0 +β1(LN DBH))

where bm = total aboveground biomass (kg) for trees 2.5-cm d.b.h. and larger d.b.h. = diameter at breast height (cm) Exp = exponential function ln = natural log base “e” (2.718282)

Derived from Jenkins et al. 2003

Documents

MO4.L09 - DIGITAL BEAMFORMING SAR (DBSAR) FOR BIOMASS ESTIMATION