scholarly journals Removal of ‘strip noise’ in radio-echo sounding data using combined wavelet and 2-D DFT filtering

2019 ◽  
Vol 61 (81) ◽  
pp. 124-134
Author(s):  
Bangbing Wang ◽  
Bo Sun ◽  
Jiaxin Wang ◽  
Jamin Greenbaum ◽  
Jingxue Guo ◽  
...  
Keyword(s):  
Wavelet Transforms ◽  
Radar Data ◽  
Discrete Wavelet ◽  
Multi Scale ◽  
Ice Surface ◽  
Fourier Filtering ◽  
Radio Echo Sounding ◽  
Instrument Noise ◽  
Echo Sounding

ABSTRACTRadio-echo sounding (RES) can be used to understand ice-sheet processes, englacial flow structures and bed properties, making it one of the most popular tools in glaciological exploration. However, RES data are often subject to ‘strip noise’, caused by internal instrument noise and interference, and/or external environmental interference, which can hamper measurement and interpretation. For example, strip noise can result in reduced power from the bed, affecting the quality of ice thickness measurements and the characterization of subglacial conditions. Here, we present a method for removing strip noise based on combined wavelet and two-dimensional (2-D) Fourier filtering. First, we implement discrete wavelet decomposition on RES data to obtain multi-scale wavelet components. Then, 2-D discrete Fourier transform (DFT) spectral analysis is performed on components containing the noise. In the Fourier domain, the 2-D DFT spectrum of strip noise keeps its linear features and can be removed with a ‘targeted masking’ operation. Finally, inverse wavelet transforms are performed on all wavelet components, including strip-removed components, to restore the data with enhanced fidelity. Model tests and field-data processing demonstrate the method removes strip noise well and, incidentally, can remove the strong first reflector from the ice surface, thus improving the general quality of radar data.

scholarly journals The newly developed airborne radio-echo sounding system of the AWI as a glaciological tool

1999 ◽  
Vol 29 ◽  
pp. 231-238 ◽  
Author(s):  
U. Nixdorf ◽  
D. Steinhage ◽  
U. Meyer ◽  
L. Hempel ◽  
M. Jenett ◽  
...  
Keyword(s):  
Digital Data ◽  
Radar Signal ◽  
Ice Shelves ◽  
System Sensitivity ◽  
Ice Caps ◽  
Radio Echo Sounding ◽  
Recorded Data ◽  
Along Track ◽  
Echo Sounding

AbstractSince 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo sounding system for remote-sensing studies of the polar ice caps in Antarctica and in Greenland. It is used to map ice thicknesses and internal layernigs of glaciers, ice sheets and ice shelves, and is capable of penetrating ice thicknesses of up to 4 km. The system was designed and built by AWI in cooperation with Aerodata Flugmeßtechnik GmbH, Technische Umversitat Hamburg-Harburg and the Deutsches Zentrum fur Luft- und Raumfahrt e.V. The system uses state-of-the-art techniques, and results in high vertical (5 m) as well as along-track (3.25 m) resolution. The radar signal is a 150 MHz burst with a duration of 60 or 600 ns. The peak power is 1.6 kW, and the system sensitivity is 190 dB. The short backfire principle has been adopted and optimized for antennae used on Polar2, a Dormer 228-100 aircraft, resulting in an antenna gain of 14 dB each. Digital data recording allows further processing. The quality of the recorded data can be monitored on screen and as online analogue plots during the flight.

scholarly journals Ice-volume changes (1936–1990) and structure of Aldegondabreen, Spitsbergen

2005 ◽  
Vol 42 ◽  
pp. 158-162 ◽  
Author(s):  
F.J. Navarro ◽  
A.F. Glazovsky ◽  
Yu.Ya. Macheret ◽  
E.V. Vasilenko ◽  
M.I. Corcuera ◽  
...  
Keyword(s):  
Radar Data ◽  
Ice Age ◽  
Aerial Photographs ◽  
Joint Analysis ◽  
Topographic Map ◽  
Ice Volume ◽  
Radio Echo Sounding ◽  
Loss Of Mass ◽  
Elevation Model ◽  
Echo Sounding

AbstractAldegondabreen is a small valley glacier, ending on land, located in the Grønfjorden area of Spitsbergen, Svalbard. Airborne radio-echo sounding in 1974/75, using a 440 MHz radar, revealed a polythermal two-layered structure, which has been confirmed by detailed ground-based radio-echo sounding done in 1999 using a 15 MHz monopulse radar. The 1999 radar data reveal an upper cold layer extending down to 90m depth in the southern part of the glacier, where the thickest ice (216 m) was also found. A repeated pattern of diffractions from the southern part of the glacier, at depths of 50–80 m and dipping down-glacier, has been interpreted as an englacial channel which originates in the temperate ice. From joint analysis of the 1936 topographic map, a digital elevation model constructed from 1990 aerial photographs and the subglacial topography determined from radar data, a severe loss of mass during the period 1936–90 has been estimated: a glacier tongue retreat of 930 m, a decrease in area from 8.9 to 7.6 km2, in average ice thickness from 101 to 73 m and in ice volume from 0.950 to 0.558 km3, which are equivalent to an average annual balance of –0.7 mw.e. This is comparable with the only available data of net mass balance for Aldegondabreen (–1.1 and –1.35m w.e. for the balance years 1976/77 and 2002/03) and consistent with the 0.27˚C increase in mean summer air temperature in this zone during 1936–90, as well as the warming in Spitsbergen following the end of the Little Ice Age (LIA), and the general glacier recession trend observed in this region.

scholarly journals An Automatic Detection by Classification of Cracked Pixels or Noncracked Pixels in Road Surface

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Khaddouj Taifi ◽  
Naima Taifi ◽  
Es-said Azougaghe ◽  
Said Safi
Keyword(s):  
Wavelet Transforms ◽  
Crack Detection ◽  
Automatic Detection ◽  
Detection Algorithm ◽  
Essential Elements ◽  
Road Surface ◽  
Discrete Wavelet ◽  
Second Phase ◽  
The Road

Automatic detection and monitoring of the condition of cracks in the road surface are essential elements to ensure road safety and quality of service. A crack detection method based on wavelet transforms (2D-DWT) and Jerman enhancement filter is used. This paper presents different contributions corresponding to the three phases of the proposed system. The first phase presents the contrast enhancement technique to improve the quality of roads surface image. The second phase proposes an effective detection algorithm using discrete wavelet (2D-DWT) with “db8” and two-level sub-band decomposition. Finally, in the third phase, the Jerman enhancement filter is usually used with different parameters of the control response uniformity “ τ ” to enhance for cracks detection. The experimental results in this article provide very powerful results and the comparisons with five existing methods show the effectiveness of the proposed technique to validate the recognition of surface cracks.

scholarly journals Coherent large beamwidth processing of radio-echo sounding data

2018 ◽  
Vol 12 (9) ◽  
pp. 2969-2979 ◽  
Author(s):  
Anton Heister ◽  
Rolf Scheiber
Keyword(s):  
Ice Sheets ◽  
Internal Layers ◽  
Spectral Filtering ◽  
Polar Ice ◽  
Bed Topography ◽  
Ice Surface ◽  
Radio Echo Sounding ◽  
Polar Ice Sheets ◽  
Slope Estimation ◽  
Echo Sounding

Abstract. Coherent processing of radio-echo sounding data of polar ice sheets is known to provide an indication of bedrock properties and detection of internal layers. We investigate the benefits of coherent processing of a large azimuth beamwidth to retrieve and characterize the orientation and angular backscattering properties of the surface and subsurface features. MCRDS data acquired over two distinct test areas in Greenland are used to demonstrate the specular backscattering properties of the ice surface and of the internal layers, as well as the much wider angular response of the bedrock. The coupling of internal layers' orientation with the bed topography is shown to increase with depth. Spectral filtering can be used to increase the SNR of the internal layers and mitigate the surface multiple. The variance of the bed backscattering can be used to characterize the bed return specularity. The use of the SAR-focused RES data ensures the correct azimuth positioning of the internal layers for the subsequent slope estimation.

scholarly journals Internal Reflecting Horizons in Spitsbergen Glaciers

1987 ◽  
Vol 9 ◽  
pp. 5-10 ◽  
Author(s):  
J. L. Bamber
Keyword(s):  
Ice Core ◽  
Entire Length ◽  
Internal Layer ◽  
Reflection Coefficients ◽  
Constant Depth ◽  
Strength Data ◽  
Ice Surface ◽  
Radio Echo Sounding ◽  
Echo Sounding

A single pronounced internal reflecting horizon has been observed on radio echo-sounding from over 30 glaciers in Spitsbergen. They are often present along the entire length of the glacier, remaining at a fairly constant depth (100–200 m) below the ice surface. Echo-strength data from radio echo-sounding have been used to obtain reflection coefficients, for these horizons, of between -15 and -25 dB. Combined with results of ice-core studies, the possible causes of this internal layer are investigated. The presence of water is found to be the most likely explanation, indicating the existence, at depth, of a layer of temperate ice.

scholarly journals Benefits of Coherent Large Beamwidth Processing of Radio-Echo Sounding Data

2018 ◽  
Author(s):  
Anton Heister ◽  
Rolf Scheiber
Keyword(s):  
Ice Sheets ◽  
Internal Layers ◽  
Spectral Filtering ◽  
Polar Ice ◽  
Angular Response ◽  
Bed Topography ◽  
Ice Surface ◽  
Radio Echo Sounding ◽  
Polar Ice Sheets ◽  
Echo Sounding

Abstract. Coherent processing of radio echo sounding data of polar ice sheets is known to provide indication of bedrock properties and detection of internal layers. We investigate the benefits of coherent processing of a large azimuth beamwidth to retrieve and characterize the orientation and angular backscattering properties of the surface and subsurface features. MCoRDS data acquired over two distinct test areas in Greenland are used to demonstrate the specular backscattering properties of the ice surface and of the internal layers, as well as the much wider angular response of the bedrock. The coupling of internal layers' orientation with the bed topography is shown to increase with depth. Spectral filtering can be used to increase the SNR of the internal layers and for mitigating the surface multiple.

Surface and Bedrock Topography of Ice Caps in Iceland, Mapped by Radio Echo-Sounding

1986 ◽  
Vol 8 ◽  
pp. 11-18 ◽  
Author(s):  
Helgi Björnsson
Keyword(s):  
Surface Elevation ◽  
Ice Thickness ◽  
Volcanic Complex ◽  
Glacier Surface ◽  
Ice Caps ◽  
Ice Cap ◽  
North East ◽  
Ice Surface ◽  
Radio Echo Sounding ◽  
Echo Sounding

Since 1977, large areas on western Vatnajökull have been surveyed by ground-based, radio echo-sounding and the whole ice cap, HofsjökuIl, was surveyed in 1983. Detailed maps of the glacier-surface elevation and the sub-ice bedrock have been compiled. The instrumentation includes a 2–5 MHz, mono-pulse echo-sounder, for continuous profiling, a satellite geoceiver and Loran-C equipment, for navigation, and a precision pressure altimeter. The maps of western Vatnajökull cover about 1500 km2 and are compiled from 1500 km-long sounding lines, which yielded about 50 000 data points for ice thickness and 20 000 points for ice-surface elevation. The maps of HofsjökuIl cover 923 km2, the sounding lines were 1350 km long; 42 000 points were used for determining ice thickness and 30 000 for surface elevation. The maps obtained from these data are the first ones of the ice caps with surface elevation of known accuracy. The bedrock map of western Vatnajökull shows details of volcanic ridges and subglacial valleys, running north-east to south-west, as well as the central, volcanic complexes, Hamarinn, Bárdarbunga, and Grimsvtön and the related fissure swarms. The map of Hofsjökull reveals a large volcanic complex, with a 650 m deep caldera. The landforms in southern Hofsjökull are predominantly aligned from north to south, but those in the northern ice cap run north by 25° east.

scholarly journals Radio-Echo Sounding of Mountain Glaciers

1975 ◽  
Vol 15 (73) ◽  
pp. 471-471
Author(s):  
I. A. Zotikov ◽  
V. S. Luchininov ◽  
Yu. Ya. Macheket ◽  
L. A. Suchanov
Keyword(s):  
Geophysical Methods ◽  
Polar Urals ◽  
Mountain Glaciers ◽  
Ice Surface ◽  
Radio Echo Sounding ◽  
Thermal Drilling ◽  
Central Caucasus ◽  
Subglacial Topography ◽  
Being Moved ◽  
Echo Sounding

AbstractExperiments on radio-echo sounding of mountain glaciers have been done on Lednik Marukh (west Caucasus), Lednik Bezingy and Lednik Dzhankuat (central Caucasus), Lednik Gergety (east Caucasus), and Lednik IGAN (Polar Urals) in 1967-71 as a part of the I.H.D. programme. Radio altimeters operating at a frequency of 440 MHz with a pulse duration 0.5 μ5 and with an assumed radio-echo system performance of 130 dB were used. The apparatus was operated from the ice surface (using sledge or vehicle) and partly from a helicopter. Some measurements have been made while the apparatus was being moved continuously along longitudal and transverse profiles of the glacier. Some of the measurements have been made at separate points on the glacier. The methods of measurement and interpretation have been worked out. Data on ice thickness, subglacial topography, and internal structure of some mountain glaciers have been obtained and compared with data got using other geophysical methods and thermal drilling. There is agreement between the results.

scholarly journals Internal Reflecting Horizons in Spitsbergen Glaciers

1987 ◽  
Vol 9 ◽  
pp. 5-10 ◽  
Author(s):  
J. L. Bamber
Keyword(s):  
Ice Core ◽  
Entire Length ◽  
Internal Layer ◽  
Reflection Coefficients ◽  
Constant Depth ◽  
Strength Data ◽  
Ice Surface ◽  
Radio Echo Sounding ◽  
Echo Sounding

A single pronounced internal reflecting horizon has been observed on radio echo-sounding from over 30 glaciers in Spitsbergen. They are often present along the entire length of the glacier, remaining at a fairly constant depth (100–200 m) below the ice surface. Echo-strength data from radio echo-sounding have been used to obtain reflection coefficients, for these horizons, of between -15 and -25 dB. Combined with results of ice-core studies, the possible causes of this internal layer are investigated. The presence of water is found to be the most likely explanation, indicating the existence, at depth, of a layer of temperate ice.

scholarly journals A Digital Radio Echo-Sounding and Navigation Recording System

1987 ◽  
Vol 9 ◽  
pp. 81-84 ◽  
Author(s):  
M.R. Gorman ◽  
A.P.R. Cooper
Keyword(s):  
Radar Data ◽  
Recording System ◽  
Data Handling ◽  
Photographic Recording ◽  
Digital Radio ◽  
Radio Echo Sounding ◽  
Versatile Tool ◽  
Polar Research Institute ◽  
Magnetic Tape Recording ◽  
Echo Sounding

The Scott Polar Research Institute (SPRI) Mk IV 60 MHz radio echo-sounding (RES) system has proven itself to be a most effective and versatile tool in glaciology. During the last 15 years, it has been used from a variety of platforms, both surface and airborne, and over a range of ice thicknesses from 4000 m to 100 m. However, the photographic recording methods used during this period were felt to be increasingly outdated in the context of modern data handling procedures. Accordingly, in late 1982 the Mk IV system was modified to incorporate fast digitizing of the RES receiver output, with microcomputer-controlled magnetic-tape recording of both the radar data and navigational inputs (Drewry and Liestøl 1985). The new system will be described, along with the improvements in data processing which have resulted from its use.

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