1. Detection of Areas of Basal Melt from RES Data
EECS 725
Detection of Areas of Basal Melt from RES Data
Manjish Adhikari

2. Retreat of ice sheet inland a major concern
Jacobshavn Isbrae, Greenland
Source:

3. Ice Sheet Dynamics
Ice sheet dynamics play major role in explaining glaciers and melting
Ice loss due to breaking or sliding of ice into the sea
Ice motion affected by temperature and strength of bases
Ice sliding due to basal melt
Basal melts due to increase in pressure which lowers MP of water and also thermal insulation

4. Data Collection- MCoRDS 2
Data collected using MCoRDS 2 nadir-looking radar developed by the Center for Remote Sensing of Ice Sheets (CReSIS) flown over Greenland and Antarctica to map ice sheet on P3 usually 480m above ice surface
Bandwidth: MHz
Tx power: 1050 W , Linear Up Chirp
PRF: Hz
Signal Duration: 1 and 10 µs(Low Altitude) 30 µs (High Altitude)
Waveform: Eight channel chirp generation
Acquisition: Sixteen channels (fifteen used),
14 bit ADC at 111 MHz bandpass sampling
data.cresis.ku.edu/data/rds/rds_readme.pdf

5. MCORDS 2 Dynamic Range: waveform playlist
Rx Aperture: Three (2 wavelength, 3.5 wavelength, and 2 wavelength ) apertures, baseline of 6.4 m between each aperture
Tx Aperture: 3.5 wavelength aperture; fully programmable
Mixed monostatic and bistatic tx/rx
Data rate: 3 2 MB/sec per channel
Range resolution: for 20 Mhz bandwidth : 3.7 m without windowing and 6.5 m with windowing
Along track resolution: 4.8 m with βx=10 deg for single look complex (SLC) SAR-processed image
data.cresis.ku.edu/data/rds/rds_readme.pdf

6. DATA PROCESSING Data converted into echograms
Initial data processing performed in the
field uses the Quicklook data samples for
a fast estimate of the
echogram clarity
Echogram is then traced for surface and
bed using layer tracker
Data also contains information Elevation,
GPS_time Latitude Longitude

7. Methods
Radar echo strength or reflectivity from bed correlated with the permittivity of medium
High reflection coefficient for ice/water interface than frozen bed/rock interface
After removing for other effects higher intensity values correlate with basal melt
Melt water reflectivity dB higher than frozen bed

8. Radar Equation
Bed echo strength (P) is function of radar system parameters(S), geometric spreading loss(G), bed reflectivity(R), englacial attenuation (L) [𝑃] 𝑑𝐵 = [𝑆] 𝑑𝐵 − [𝐺] 𝑑𝐵 + [𝑅] 𝑑𝐵 − 𝐿 𝑑𝐵

9. Corrections to Intensity
Interference and Fading: Coherent integration applied upto 4 m and incoherent averaging upto ~200 m to remove these effects
Geometrical Spreading: [𝐺] 𝑑𝐵 = 2[2 ℎ+ 𝑧 𝑛 𝑖 ] 𝑑𝐵
Dielectric Loss: Intensity reduces with propagation through ice , variable with area but this method assumes constant attenuation rate so vary with depth only;
For Greenland: 𝐵=2.3∗ 3000 𝐻 𝑑𝐵 𝑝𝑒𝑟 100𝑚 (B=1.4±0.1 for 3000m and B=2.3±0.1 for 1000m)

10. 𝐼 𝐶𝑂 = 𝐷 𝑖𝑛𝑡 <| 𝑋 𝑖𝑛𝑡 | 𝜓 𝐷,𝑥 | 2 >𝑑𝐷 𝐷 𝑖𝑛𝑡 𝑋 𝑖𝑛𝑡 |𝜓(𝐷,𝑥| 2 𝑑𝑥𝑑𝐷
Reflection Abruptness: Sudden change in intensity from low to high denote change in material.
𝐼 𝑎𝑏𝑟 = 𝑃 𝑝𝑒𝑎𝑘 𝑃 𝑎𝑔 (𝑥) = ( 𝑝 𝑋 ) 𝑝𝑒𝑎𝑘 { 𝐷 𝑖𝑛𝑡 𝑃} 𝑋
Normally lies between 0.05 and 0.5
Coherence Index: Measure of smoothness of bed or flat interface
𝐼 𝐶𝑂 = 𝐷 𝑖𝑛𝑡 <| 𝑋 𝑖𝑛𝑡 | 𝜓 𝐷,𝑥 | 2 >𝑑𝐷 𝐷 𝑖𝑛𝑡 𝑋 𝑖𝑛𝑡 |𝜓(𝐷,𝑥| 2 𝑑𝑥𝑑𝐷

11. Results and Analysis
Areas with high intensity values, high abruptive index and high coherence index correlate with presence of basal melt.
Areas cross checked with geophysics of the location for validation

12. References
[1].Oswald, and Gogineni, Recovery of subglacial water extent from Greenland radar survey data, Journal of Glaciology, Vol. 54, No. 184, 2008
[2]. Leuschen, Carl, Prasad Gogineni, Richard Hale, John Paden, Fernando Rodriguez, Ben Panzer, Daniel Gomez. 2014, updated 2016. IceBridge MCoRDS L1B Geolocated Radar Echo Strength Profiles, Version 2,
[3]. Oswald, and Gogineni Mapping Basal Melt Under the Northern Greenland Ice Sheet, Ieee Transactions On Geoscience And Remote Sensing, Vol. 50, No. 2, February 2012
[4]. Center for Remote Sensing of Ice sheets (CReSIS) data.cresis.ku.edu/data/rds/rds_readme.pdf

13. Thank you