scholarly journals Airborne Electromagnetic Sea Ice Thickness Sounding in Shallow, Brackish Water Environments of the Caspian and Baltic Seas

2006 ◽  
Author(s):  
Christian Haas
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Brackish Water ◽  
Low Frequency ◽  
Ice Thickness ◽  
Sea Ice Thickness ◽  
Sea Floor ◽  
Airborne Electromagnetic ◽  
The Baltic ◽  
Engineering Projects

Ice engineering projects often rely on the knowledge of ice thickness in shallow, brackish water like in the Baltic and Caspian Seas. By means of field data and model results, the paper shows that helicopter-borne electromagnetic induction measurements using frequencies of 3.68 and 112 kHz can yield accurate thickness estimates with salinities as low as 3 ppt. The higher frequency yields the strongest EM signals. In addition, in shallow water the higher frequency is less sensitive to the sea floor signal, and can thus be used in water depths as shallow as 4 to 6 m, depending on flying altitude. Because the low frequency signal is very sensitive on shallow water depth, a combination of both signals will allow the retrieval of both ice thickness and water depth.

Geophysical imaging of Silurian carbonates by use of ground and airborne electromagnetic and radiometric methods on the island of Gotland, Sweden

2015 ◽  
Vol 3 (3) ◽  
pp. SY1-SY11 ◽  
Author(s):  
Lena Persson ◽  
Mikael Erlström
Keyword(s):  
Carbonate Platform ◽  
Low Frequency ◽  
Rock Types ◽  
Transient Electromagnetic ◽  
Geophysical Surveys ◽  
Airborne Electromagnetic ◽  
The Difference ◽  
Geophysical Imaging ◽  
Definition Of ◽  
The Baltic

The island of Gotland in the Baltic Sea exhibits rock types dominated by limestone and marlstone, deposited in a Silurian carbonate platform environment. The strata are extensively exposed in outcrops, quarries, and coastal cliff sections. Low-lying marlstone-dominated areas are separated by highs dominated by limestone. The surface bedrock is well known, but the subsurface composition down to a 100-m depth has, until recent deployment of modern geophysical measurements, been largely unknown. Our geophysical surveys and methods were performed with the aim to evaluate their usefulness in characterizing the upper 100 m of the bedrock in a carbonate-dominated bedrock setting. The surveys were performed in connection to a bedrock mapping project including geologic and geophysical investigations. The airborne techniques complemented by ground measurements and correlation with outcrops and boreholes resulted in a definition of bedrock boundaries and especially subsurface characterization of bedding sequences. The airborne electromagnetic (very low frequency) survey was accompanied by radio magnetotelluric (RMT) measurement on the ground along several profiles. The difference in resistivity between high-resistive limestone overlaying a more conductive marlstone gave favorable conditions for this type of survey. The results have so far given new and valuable information on the thickness of the limestone as well as the distinction of lateral changes of the bedrock related to the depositional setting. The RMT measurements have made it possible in a new way to remotely map out bedding sequences in carbonates and to detect saline groundwater and fracture zones. In addition, a recently performed airborne transient electromagnetic survey contributed to the interpretation of the RMT measurements that we evaluated. The applied geophysical methodology and correlation with outcrops revealed carbonate bedrock with geophysical properties, enabling a better understanding concerning the groundwater conditions, limestone resources, and radon situation on the island of Gotland.

How to Deal With Basin Modes When Generating Irregular Waves on Shallow Water

2016 ◽  
Author(s):  
Sanne van Essen ◽  
Willemijn Pauw ◽  
Joris van den Berg
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Water Waves ◽  
Low Frequency ◽  
Effective Length ◽  
Irregular Waves ◽  
Natural Modes ◽  
Wave Basin ◽  
Basin Geometry ◽  
Basin Mode

Modeling shallow-water waves in a basin with a finite length and width introduces challenges related to low-frequency (LF) waves, especially for testing of moored vessels with long natural periods. Waves in this frequency range are also present in reality, as for instance bound set-down waves and unbound free waves formed by the geometry bathymetry. In model basins, additional unwanted LF wave components will be formed as a side-product of the wave generation and due to the basin geometry though. Standing waves over the basin length and width (basin modes) can generally be identified, which are difficult to dampen using beaches. This is the case for every wave basin, as they all have finite dimensions. Moored structures generally have natural frequencies in the LF range, which may be excited by basin modes with similar frequencies. It is therefore important to understand the natural modes of a basin before tests with moored structures in shallow water are done. The energy of these basin modes increases and their natural frequency decreases with decreasing water depth (waves travel slower in shallow water). Generally, it can be said that the issues with basin modes are present on very shallow water (typically ∼15–30 m water depth full-scale for structures with a length around 200 m at a scale around 1 to 40). The smaller the basin for the same water depth, the higher the basin mode frequencies and the higher the likelihood of resonance problems. The energy and frequencies of the basin modes and their relevance for specific tests depend on the effective length and width of the basin, the water depth, wave conditions and the (mooring stiffness of) the structure under consideration. The influence of these variables is evaluated in the current study. Tests were done in MARIN’s Offshore Basin (OB), but most of the results are also expected to be applicable to other basins. The observed basin mode frequencies during these tests were compared to the theoretical values, and an overview of the unwanted LF wave content as a function of water depth, wave height and period is presented. The energy and shape of individual basin modes is also discussed. Considering these results, a practical approach for future basin projects on shallow water is described.

scholarly journals Recent summer sea ice thickness surveys in Fram Strait and associated ice volume fluxes

2016 ◽  
Vol 10 (2) ◽  
pp. 523-534 ◽  
Author(s):  
T. Krumpen ◽  
R. Gerdes ◽  
C. Haas ◽  
S. Hendricks ◽  
A. Herber ◽  
...  
Keyword(s):  
Sea Ice ◽  
Satellite Data ◽  
Primary Source ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Ice Thickness ◽  
Fram Strait ◽  
Data Set ◽  
Sea Ice Thickness ◽  
Airborne Electromagnetic

Abstract. Fram Strait is the main gateway for sea ice export out of the Arctic Ocean, and therefore observations there give insight into the composition and properties of Arctic sea ice in general and how it varies over time. A data set of ground-based and airborne electromagnetic ice thickness measurements collected during summer between 2001 and 2012 is presented here, including long transects well into the southern part of the Transpolar Drift obtained using fixed-wing aircrafts. The primary source of the surveyed sea ice leaving Fram Strait is the Laptev Sea and its age has decreased from 3 to 2 years between 1990 and 2012. The thickness data consistently also show a general thinning of sea ice for the last decade, with a decrease in modal thickness of second year and multiyear ice, and a decrease in mean thickness and fraction of ice thicker than 3 m. Local melting in the strait was investigated in two surveys performed in the downstream direction, showing a decrease in sea ice thickness of 0.19 m degree−1 latitude south of 81° N. Further north variability in ice thickness is more related to differences in age and deformation. The thickness observations were combined with ice area export estimates to calculate summer volume fluxes of sea ice. While satellite data show that monthly ice area export had positive trends since 1980 (10.9  ×  103 km2 decade−1), the summer (July and August) ice area export is low with high uncertainties. The average volume export amounts to 16.78 km3. Naturally, the volume flux estimates are limited to the period when airborne thickness surveys are available. Nevertheless, we could show that the combination of satellite data and airborne observations can be used to determine volume fluxes through Fram Strait and as such, can be used to bridge the lack of satellite-based sea ice thickness information in summer.

scholarly journals Recent summer sea ice thickness surveys in the Fram Strait and associated volume fluxes

2015 ◽  
Vol 9 (5) ◽  
pp. 5171-5202 ◽  
Author(s):  
T. Krumpen ◽  
R. Gerdes ◽  
C. Haas ◽  
S. Hendricks ◽  
A. Herber ◽  
...  
Keyword(s):  
Sea Ice ◽  
Source Area ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Ice Thickness ◽  
Fram Strait ◽  
Data Set ◽  
Sea Ice Thickness ◽  
Airborne Electromagnetic ◽  
Transpolar Drift

Abstract. Fram Strait is the main gateway for sea ice export out of the Arctic Ocean, and therefore observations there give insight into composition and properties of Arctic sea ice in general and how it varies over time. An extensive data set of ground-based and airborne electromagnetic ice thickness measurements collected between 2001 and 2012 is presented here, including long transects well into the southern part of the Transpolar Drift obtained using fixed-wing aircrafts. The source area for the surveyed ice is primarily the Laptev Sea, and the estimated age is consistent with a decreased from 3 to 2 years between 1990 and 2012. The data consistently also show a general thinning for the last decade, with a decrease in modal thickness of second year and multiyear ice, and a decrease in mean thickness and fraction of ice thicker than 3 m. Local melting in the strait was investigated in two surveys performed in the downstream direction, showing a decrease of 0.19 m degree−1 latitude south of 81° N probably driven by bottom melting from warm water of Atlantic origin. Further north variability in ice thickness is more related to differences in age and deformation. The thickness observations were combined with ice area export estimates to calculate summer volume fluxes of sea ice. This shows that it is possible to determine volume fluxes through Fram Strait during summer when satellite based sea ice thickness information is missing. While the ice area export based on satellite remote sensing shows positive trends since 2001, the mean fluxes during summer (July and August) are small (18 km3), and long-term trends are uncertain due to the limited surveys available.

scholarly journals Combined SMAP/SMOS Thin Sea Ice Thickness Retrieval

2017 ◽  
Author(s):  
Cătălin Pațilea ◽  
Georg Heygster ◽  
Marcus Huntemann ◽  
Gunnar Spreen
Keyword(s):  
Soil Moisture ◽  
Sea Ice ◽  
Incidence Angle ◽  
Low Frequency ◽  
Retrieval Algorithm ◽  
Ice Thickness ◽  
Polar Regions ◽  
Sea Ice Thickness ◽  
Brightness Temperatures ◽  
Ocean Salinity

Abstract. The spaceborne passive microwave sensors Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) provide brightness temperature data at L-band (1.4 GHz). At this low frequency the atmosphere is close to transparent and in polar regions the thickness of thin sea ice can be derived. SMOS data covers a large incidence angle range whereas SMAP observes at a fixed 40° incidence angle which makes thin sea ice thickness retrieval more stable as incidence angle effects do not have to be taken into account. Here we transfer a retrieval algorithm for thickness of thin sea ice (up to 50 cm) from SMOS data at 40° to 50° incidence angle to the fixed incidence angle of SMAP. Now the SMOS brightness temperatures (TBs) at a given incidence angle are estimated using empirical fit functions. SMAP TBs are calibrated to SMOS for providing a merged SMOS/SMAP Sea Ice Thickness product.

Sign in / Sign up

Export Citation Format

Share Document