Airborne Ice and Snow Radars (and other EM Sensors)

Robinson, Carl

Head of Airborne Sensor Technology

British Antarctic Survey,

Cambridge,

United Kingdom carob@bas.ac.uk

• Antarctica is the least understood continent

on Earth (99.6% is covered by ice up to 4.8

km thick)

WHY?

East

West

Radar a Cambridge History

•SPRI Mark2 35MHz non coherent pulse radar

(Single Otter & Porter) (1966-1967)

•Simple dipole antennas clamped to wing struts

•Z-scope recorded to 35mm film

•D Shackman & Sons Ltd. auto camera

•Dead reckoning geolocating (~30 fixes / hour)

•SPRI Mark4 60MHz 250ns pulse radar (1969-1972)

(1969-1972)

Radar Development

• SPRI radar was developed to suit BAS needs during 1974

(Hugh McPherson) for the 1974/1975 season and with minor

updates for logging of aircraft flight data was used until the last

time during the 1986/1987 season

•Radar recorded to 35mm film (Shackman)

•Cathoray tube

•Aircraft data logged (1979 Navlogger)

•Better aircraft navigation

•Radar altimeter (1974)

•Hitachi V209 oscilloscope (1980)

•Motorola TMOS transistors in Tx amplifiers (1983)

(1974-1987)

Radar Recording Improved

•Recording technology improved (1987)

•Pulnix video camera

•Panasonic NV-FS1 SVHS

•New data logger

• Land based tests (Late 80s)

• 150MHz radar (1992)

• Radar enters digital age (1993)

•Lecroy digitising scope and VME based data

processor (1993)

•Tektronix digitising scopes followed the Lecroy

•Optical disk storage

(1987-2004)

Radar Renaissance

•PASIN (Polarimetric Radar Airborne Science Instrument)

(2003)

• 150MHz Two pulse radar with polarimetric mode

• RF power 4KW

•PASIN + (2007-2014)

• Incremental updates to faster CPU and better storage

•PASIN 2 (2014-)

• 8 channel Tx / Rx 150MHz chirp pulsed radar

•Snow radars (2014-)

• 2-6 GHz bandwidth CW chirp radar

(2004-)

Airborne Radar Types

• Continuous Wave (FMCW)

• Pulsed

• Pulsed Chirp

Delta frequency equal to range

Tx Chirp

Rx Chirp

Airborne Radar

Radar System

Waveform generator

RF transmitter

RF receiver Radar data

logger

Time and position

Control and synchronisation

Power

• A scan stacked to make Z scan

• Displayed and logged

Swithinbank et al 1966 Corr et al 2010

• Processed

PASIN Radar

Radar Antenna Radar Antenna

•PASIN (Polarimetric Radar Airborne Science Instrument)

• Two pulse radar - pulse 100ns and 4us chirp

• Polarimetric mode

• Coherent

• Real time logging to USB3 hard drives

• RF power amps (4KW total)

• NI PXI / LabVIEW

•PASIN 2

• 8 channel Tx / Rx across track processing

• 16 bit (200MHz) digitising card custom FPGA

• 2GHz arbitrary wave generating (AWG) boards

Carrier Frequency 150 MHz

Bandwidth 10 MHz

Along track 10 cm

Depth resolution 8 m

PASIN Radar •PASIN (88MHz ADC clock / 198MHz DAC clock)

• Similarly Nyquist zone 2 used for Tx (fclock-baseband = 198-48 = 150MHz)

•PASIN 2 (120MHz ADC clock)

• Better ADC digitising board

• Board capable of direct AWG generation of 150MHz 18MHz BW chirp

Radar in the Gamburtsev Province Deepest Ice: 4596 metres

25 km

Thinnest Ice: 315 metres

25 km

Internal Layers

Bedrock

Ice

Bedrock

Ice

North Antarctic Gamburtsev Province Bed

Topography (Corr et al 2009)

Radar in the Gamburtsev Province

25 km

3.2

km

Bedrock

Ice

Subglacial Water Bodies?

Corr et al

Snow Radar (2-6GHz bandwidth)

• High resolution layer detail, sea ice (great scientific interest)

• Resolution is the product of bandwidth

• Depth sounding is the product of signal to noise

•Wide band antennas, Eccosorb foam

• Pentek digitiser board (common to PASIN2 with updated FPGA)

• Euvis AWG board (common to PASIN2)

Future Innovations in Ice Sounding Radar

(ALFRIS 2011)

• Warm ice surveying

• Long range Arctic / Antarctic work

• Airborne Low Frequency

Radar Imaging System

• 5MHz to 50MHz system

• Five trailing antennas

• Technology transferable

to Twin Otter

Dash 7 Platform – Radars and EM

Equipment Payload

Volume Available in Bay 1.55 m x 0.62 m x 1.2 m (lwh)

Weight 400 KG with out impact to range

(EM) Bird 3.5 m x 0.36 m (length diameter)

Power 28V 300A

Radar Advances and the Future

• Coherent radar, same phase pulse to pulse a (allow Doppler

resolution/estimation, provides less interference and signal/noise improvements compared to non-coherent processing)

• Digitisation of the return

• Advancements in electronics and computers –transistors (signal and power) > amplifiers (OP, LNA, power); CPU, high speed buses, data storage

• Modern processing - Doppler, SAR, noise cancelation

The Future? • Antennas - Ultra wide band low frequency (new materials?)

• 20 GHz AWG (direct AWG no frequency multipliers or PLL)

• Ever greater and faster storage media

• Flatter frequency RF components

• Ever better radar processing techniques

• New technology – much of the technology used crosses a wide range of disiplines

Robinson, Carl

Head of Airborne Sensor Technology

British Antarctic Survey,

Cambridge,

United Kingdom

carob@bas.ac.uk