Scott Hensley, Howard Zebker, Cathleen Jones, Paul Lundgren, Eric Fielding, Thierry Michel and Bruce Chapman.

Scott Hensley, Howard Zebker, Cathleen Jones, Scott Hensley, Howard Zebker, Cathleen Jones,

Paul Lundgren, Eric Fielding, Thierry Michel and Bruce Paul Lundgren, Eric Fielding, Thierry Michel and Bruce ChapmanChapman

UAVSAR• UAVSAR is an L-band fully polarimetric SAR employing an

electronically scanned antenna that has been designed to support a wide range of science investigations.

– Science investigations supported by UAVSAR include solid earth, cryospheric studies, vegetation mapping and land use classification, archeological research, soil moisture mapping, geology and cold land processes.

– To support science applications requiring repeat pass observations such as solid earth and vegetation applications the UAVSAR design incorporates:

• A precision autopilot developed by NASA Dryden that allows the platform to fly repeat trajectories that are mostly within a 5 m tube.

• Compensates for attitude angle changes during and between repeat tracks by electronically pointing the antenna based on attitude angle changes measured by the INU.

• UAVSAR is testing new experimental modes, e.g. the multi-squint mode whereby data is collected simultaneously at multiple squint angles to enable vector deformation measurements with a single repeat pass.

Need for Airborne RPI Instrument

• Spaceborne repeat pass radar interferometry derived deformation measurements has become a standard tool for the solid earth science and glaciological science communities.– Repeat times controlled by the the repeat orbit cycle

of spaceborne SAR systems, e.g. ERS-1,2 (35 days), Radarsat (24 days), JERS (44 days), and Envisat ( 35 days).

– Rapidly deforming features such as some volcanoes and glaciers or deformation from post seismic rebound require repeat times of a day or less to fully study the time varying nature of the deformation signal.

• Repeat pass airborne interferometric measurements are more difficult to make because– The difficulty of flying a specified trajectory with

the required accuracy– To need to compensate for pointing changes between

flight tracks

UAVSAR and Volcano Observations• Although a number of the world’s active volcanoes have continuous seismic and/or

GPS monitoring there is still a large number that are not persistently monitored.

• Placing in situ monitoring devices on volcanoes after they enter more active states can be dangerous and usually only a few such devices can be deployed leading to an under sampling of the resulting deformation.

• UAVSAR is ideally suited to making repeat pass observations of volcanic regions:

– It has a large swath in excess of 20 km with fully polarimetric observations and flies at high altitudes (> 12.5 km) with a resolution of 1.6 m in range and 1m in azimuth.

– Operates at L-band to reduce temporal decorrelation.

– It can be tasked to make repeat observations on time scales as short as 20 minutes from any desired look direction.

– It can control its flight path to be within a 10 m tube (usually within 5 m) and adjust its look direction electronically to compensate for aircraft attitude changes.

– Has a vector deformation capability whereby vector deformation (and atmospheric distortions - under investigation) can be simultaneously determined.

– Can be rapidly deployed to monitor evolving volcano hazards or routinely tasked to monitor more quiescent volcanoes.

Initial Flight Testing of UAVSAR

Antenna Overview

• 24 T/R Modules

• 3 RF Manifold Boards ASN

• 6 power only ESSs

•Differential low voltage daisy

chain signaling

•TRAC

ESS

TR1

TR2

TR3

TR4

ESS

TR9

TR10

TR11

TR12

ESS

TR5

TR6

TR7

TR8

ESS

TR13

TR14

TR15

TR16

ESS

TR17

TR18

TR19

TR20

ESS

TR21

TR22

TR23

TR24

TRAC

DC /DCAircraft

28V

CTU

RF manifold RF manifoldASNRF

Diff to single

Differential Low Voltage Signaling

Single-ended Low Voltage Signaling

Key Radar Instrument Parameters

Parameter Value

Frequency L-Band 1217.5 to 1297.5 MHz

Bandwidth 80 MHz

Resolution 1.67 m Range, 0.8 m Azimuth

Polarization Full Quad-Polarization

ADC Bits2,4,6,8,10 & 12 bit selectable

BFPQ, 180Mhz

WaveformNominal Chirp/Arbitrary

Waveform

Antenna Aperture0.5 m range/1.5 azimuth

(electrical)

Azimuth Steering Greater than ±20° (±45°

goal)

Transmit Power > 3.1 kW

Polarization Isolation

<-25 dB (<-30 dB goal)

UAVSAR Modes

CoPol MonopulseMulti-Squint Vector Deformation

Strip Mode SAR Polarimetric SAR

Example Repeat Pass Baselines

10 m Tube

5 m Tube

San Andreas Fault Repeat-Pass Baseline

80 km Datatakes on February 12 and 20 of 2008.

10 m Tube

5 m Tube

10 m Tube

5 m Tube

Repeat Pass Processing Challenges

• Repeat pass processing of airborne data is very challenging for several reasons:– First, the onboard motion metrology (INU and DGPS) are not sufficient to support automated processing of the data. Best case

the INU+GPS combination provide 3 cm antenna phase center flight path reconstruction, whereas the needed accuracy is 1 mm or less. This means residual motion between passes must be solved for from the data themselves.

– The motion compensation algorithm, which corrects the SAR data from an irregular flight path to a reference trajectory, is terrain dependent. This imposes additional processing complexity and reduces throughput.

– Effective phase center changes resulting from electronically steering the antenna must be compensated on a pulse-by-pulse basis to avoid phase discontinuities in the differential interferograms.

• Repeat pass processing presently involves a large amount of touch labor particularly with respect to the residual motion estimation. This problem is complicated due to:

– Temporal decorrelation results in loss of signal which impedes the ability to estimate residual motion.– Deformation signals in the cross line-of-sight direction couple with residual motion errors hence making estimation of residual

motion in the region where deformation is occurring extremely difficult.

Mt St Helens Photo

Mt St Helens - UAVSAR March 24, 2008

FlightDirection

> 20 km

• Fully polarimetric image of Mt St Helens collected on March 24, 2008 by the UAVSAR radar. A second acquisition was collected on March 31, 2008.

Expanded View of Caldera and Dome

AIRSAR December 2004

Mt St Helens Interferogram - 4 hour Repeat

• Since time between observations is 4.2 hours or .174 days, the estimated rate of motion for an approximate radians of phase change is

Phase (rad)

• This is a first cut interferogram - no offset measurements - no motion correction - no topography correction

Mt St Helens - UAVSAR March 24, 2008

FlightDirection

> 20 km

• Two fully polarimetric image of Mt St Helens collected on March 24, 2008 by the UAVSAR radar separated by 4 hours. A second acquisition was collected on March 31, 2008.

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

• Deformation of 37 cm/day and 15 cm/day observed on the two tongues of the glaciers in the caldera.

• Refined processing underway to look for deformation on dome.

Multi-Squint Mode Example• Data collected in the UAVSAR multi-squint mode. Yaw angle of -5.0° with azimuth steering angles of 13.6° and -6.2°.

• Anthropogenic features exhibit strong viewing angle scattering signatures.

Azimuth Steering Angle: 13.6°

Azimuth Steering Angle: -6.2°

-5°

-5°13.6°

-6.2°

UAVSAR Status• UAVSAR is an actively scanned fully polarimetric L-band SAR designed to meet a

range of remote sensing applications of interest to the science community including specific features to support repeat pass interferometry for deformation studies.

• UAVSAR platform is completing modifications to extend its range and increase the number of airports it can be deployed.

• The system is expected to be available to the general science community starting in late 2008 with a number of investigators already funded for data collections.