Detection of Areas of Basal Melt from RES Data EECS 725 Detection of Areas of Basal Melt from RES Data Manjish Adhikari 2870257

Retreat of ice sheet inland a major concern Jacobshavn Isbrae, Greenland Source: https://www.nasa.gov/

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

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: 180 -210 MHz Tx power: 1050 W , Linear Up Chirp PRF: 12000 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

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

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

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 10-15 dB higher than frozen bed

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

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+2000 𝑑𝐵 𝑝𝑒𝑟 100𝑚 (B=1.4±0.1 for 3000m and B=2.3±0.1 for 1000m)

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

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

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

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