Airborne Ice and Snow Radars (and other EM Sensors)
Robinson, Carl
Head of Airborne Sensor Technology
British Antarctic Survey,
Cambridge,
United Kingdom [email protected]
• 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)
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