Date (Creation)

2021-07-05

Date (Revision)

2021-07-05

Date (Publication)

2021-07-05

Date (released)

2021-07-05

Edition

1.0

Unique resource identifier

https://doi.org/10.5285/7c12898d-7e55-458c-ba7d-ecec8252f3b5

Codespace

doi

Unique resource identifier

GB/NERC/BAS/PDC/01520

Codespace

https://data.bas.ac.uk/

Other citation details

Please cite this item as: Jordan, T., & Robinson, C. (2021). Bed, surface elevation and ice thickness measurements derived from radar data acquired during the Thwaites Glacier airborne survey (2019/2020) (Version 1.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/7c12898d-7e55-458c-ba7d-ecec8252f3b5

Credit

No credit.

Status

Completed

Point of contact

Organisation name	Individual name	Electronic mail address	Role
British Antarctic Survey	Jordan, Tom		Author
British Antarctic Survey	Robinson, Carl		Author
NERC EDS UK Polar Data Centre		PDCServiceDesk@bas.ac.uk	Point of contact

Maintenance and update frequency

As needed

Maintenance note

Completed

Global Change Master Directory (GCMD) Science Keywords

• EARTH SCIENCE > Cryosphere > Glaciers/Ice Sheets > Glacier Elevation/Ice Sheet Elevation
• EARTH SCIENCE > Cryosphere > Glaciers/Ice Sheets > Glacier Thickness/Ice Sheet Thickness
• EARTH SCIENCE > Cryosphere > Glaciers/Ice Sheets > Glacier Topography/Ice Sheet Topography
• EARTH SCIENCE > Cryosphere > Glaciers/Ice Sheets > Ice Sheets
• EARTH SCIENCE > Land Surface > Topography

Theme

• Antarctica

• Geophysics

• ITGC

• Radar

• Thwaites Glacier

Place

• Thwaites Glacier Antarctica

GEMET - INSPIRE themes, version 1.0

• Elevation
• Land cover

Access constraints

Other restrictions

Other constraints

no limitations to public access

Access constraints

Other restrictions

Other constraints

no limitations

Use constraints

License

Other constraints

Open Government Licence v3.0

Use constraints

Other restrictions

Other constraints

This data is governed by the NERC Data Policy: https://www.ukri.org/who-we-are/nerc/our-policies-and-standards/nerc-data-policy/

Use constraints

Other restrictions

Other constraints

Further by downloading this data the user acknowledges that they agree with the NERC data policy (), and the following conditions:

1. To cite the data in any publication as follows:

DATA REFERENCE

Jordan, T., & Robinson, C. (2021). Bed, surface elevation and ice thickness measurements derived from radar data acquired during the Thwaites Glacier airborne survey (2019/2020) (Version 1.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/7C12898D-7E55-458C-BA7D-ECEC8252F3B5

2. The user recognizes the limitations of data. Use of the data is at the users' own risk, and there is no warranty as to the quality or accuracy of any data, or the fitness of the data for your intended use. The data are not necessarily fully quality assured and cannot be expected to be free from measurement uncertainty, systematic biases, or errors of interpretation or analysis, and may include inaccuracies in error margins quoted with the data.

Use constraints

Other restrictions

Other constraints

None

Unique resource identifier

url

Codespace

url

Association Type

Cross reference

Unique resource identifier

url

Codespace

url

Association Type

Larger work citation

Unique resource identifier

doi

Codespace

doi

Association Type

Cross reference

Spatial representation type

Text, table

Language

English

Character set

UTF8

Topic category

• Geoscientific information

Begin date

2019-12-24

End date

2019-12-29

Supplemental Information

It is recommended that careful attention be paid to the contents of any data, and that the author be contacted with any questions regarding appropriate use. If you find any errors or omissions, please report them to polardatacentre@bas.ac.uk.

Title

European Petroleum Survey Group (EPSG) Geodetic Parameter Registry

Date (Publication)

2008-11-12

Cited responsible party

Organisation name	Individual name	Electronic mail address	Role
European Petroleum Survey Group		EPSGadministrator@iogp.org	Publisher

Unique resource identifier

urn:ogc:def:crs:EPSG::3031

Version

6.18.3

Hierarchy level

Dataset

Statement

Methodology:

The PASIN airborne radar system was run in polametric mode for the 2019/20 Thwaites field campaign, meaning the 4 antennas in each wing array were orientated at 90 degrees to each other. The belly antenna initially added an additional 4 antenna array operating in receive mode only. The belly antenna ceased to function after the initial input flight (T05).

The PASIN system transmitted 5 separate pulses from the wing arrays as follows; Port 4 microseconds chirp; Starboard 4 microseconds chirp; Port 4 microseconds chirp 180deg phase shift; Starboard 4 microseconds chirp 180deg phase shift; Port 1 microseconds chirp. Data for every antenna and pulse is recorded separately, in 20 second segments.

For picking the along-track bed elevation, only data from the port antenna array was used. Data from all the port antennas was combined, and the 4 microseconds and microseconds 180° phase shift pulses were combined to enhance the array gain and minimise coherent noise. The use of the same transmit/receive array theoretically minimises the power loss due to cross polarisation of the opposite wing. Along-track SAR focusing was applied to the combined port wing data. The final data was output as a port to port (P2P) segy file. The segy files for each flight were then imported into the Promax seismic processing package. Down trace 'time' is simply the sample number across the 64 microseconds window, digitised at 120 MHz (i.e. max sample number = 7680 = 64 microseconds). Weighted trace mixing across 5 traces was applied to improve the signal to noise ratio of the data and down-trace automatic gain control was applied to reveal low amplitude returns from deeper reflectors. An initial window ~100 samples above the bed reflection was manually defined (top mute). An automated first break pick algorithm was then run to locate the precise bed return below the top mute. Subsequent manual picking removed un-realistic spikes, and selected the most physically appropriate bed surface in cases where multiple reflections were seen close to the bed. Generally the shallowest reflector was assumed to be the bed, as off-axis reflectors would likely appear later (deeper) in the section. In some cases strong reflectors which appeared deeper were chosen, with shallower week reflectors assumed to reflect entrained debris, accreted ice, or un-compensated refraction hyperbole close to the bed.

The PASIN radar system does not resolve the ice surface well. Range to surface from coincident LIDAR data, or calculated from an accurate DEM is therefore preferred. However, to estimate ice thickness and hence correct bed elevation, the location of the surface reflector in the radargram must be known. To calculate the theoretical surface pick location from the LIDAR or DEM range to ground these measurements must be calibrated. To do this the ice surface location for a single flight (T05) was picked from the Port to Starboard (P2S) radar dataset. Use of this dataset avoided the problem of the transmit pulse and switching period overlapping with the surface reflection. The location of the surface reflector was picked in Promax following a similar approach to the bed, with an additional bottom mute defined ~100 samples below the surface reflection. The Promax surface pick was then plotted against the LIDAR range to ground and a linear trend fit to the data. The resulting slope and offset was used to calculate the theoretical location of the surface in all the subsequent radargrams from either LIDAR or DEM derived range to ground. Where possible the range to ground value was from LIDAR data, or interpolated from the mean Lidar elevation within ~700 m. Where no LIDAR data was available within ~1400 m horizontally the REMA DEM was used, with a smooth interpolation between the surface elevation data sources.

To calculate ice thickness the difference between the bed pick and theoretica...(27)

Data collection:

Data was collected using the BAS aerogeophysicaly equipped twin otter VP-FBL. The radar system was the PASIN polametric radar.

** Antenna configuration:

8 folded dipole elements:

4 transmitters (port side)

4 receivers (starboard side)

Antenna gain: 11 dBi (with 4 elements)

Transmit power: 1 kW into each 4 antennae

Maximum transmit duty cycle: 10% at full power (4 x 1 kW)

** Radar receiver configuration:

Receiver vertical sampling frequency: 22 MHz (resulting in sampling interval of 45.4546 ns)

Receiver coherent stacking: 25

Receiver digital filtering: -50 dBc at Nyquist (11 MHz)

Effective PRF: 312.5 Hz (post-hardware stacking)

Sustained data rate: 10.56 Mbytes/second

Data quality:

Analysis of 52 crossover points within the survey area indicates a standard deviation for the bed elevation of ~22m, which is in-line with the values suggested for previous radar surveys. LIDAR-derived surface elevation has a crossover error of ~10 m. The relatively high value is attributed to the use of LIDAR nadir range to ground un-corrected for aircraft roll, pitch and yaw.

- Line spacing: ~15 km (designed to inter-leave with previous surveys)

- Trace spacing (post-processed data): ~24 m

- Vertical resolution: ~8.4 m

- Radar centre frequency: 150 MHz

- Radar bandwidth: 12 MHz

- Radar Receiver vertical sampling frequency: 22 MHz

- Absolute GPS positional accuracy: ~0.1 m (relative accuracy is one order of magnitude better). Banking angle was limited to 10 deg during aircraft turns to avoid phase issues between GPS receiver and transmitter.

Metadata

File identifier

7c12898d-7e55-458c-ba7d-ecec8252f3b5 XML

Metadata language

English

Character set

UTF8

Hierarchy level

Dataset

Hierarchy level name

dataset

Date stamp

2021-07-05

Metadata standard name

ISO 19115 Geographic Information - Metadata

Metadata standard version

ISO 19115:2003(E)

Metadata author

Organisation name	Individual name	Electronic mail address	Role
NERC EDS UK Polar Data Centre		polardatacentre@bas.ac.uk	Point of contact