pattern recognition of air photographs for estimation of snow reserves a certain snow covered area determined from air photographs in different years can contain different volumes of snow the pattern recognition of snow fields reveals whether the snow reserves are relatively high or low for the given snow coverage it also signals a short terra increase of the snow covered area by summer snowfall

size shape and spatial arrangement of mega scale glacial lineations from a large and diverse dataset mega scale glacial lineations msgls are a characteristic landform on ice stream beds solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this in turn influences the dynamics of ice streams however a comprehensive and detailed characterization of this landform s size shape and spatial arrangement which might serve to test and refine formational theories is largely lacking this paper presents a detailed morphometric analysis and comparison of 4043 msgls from eight palaeo ice stream settings three offshore norway and antarctica four onshore canada and one from under a modern ice stream in west antarctica the length of msgls is lower than previously suggested mode 1000 2000 m median 2892 m and they initiate and terminate at various locations on an ice stream bed their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity 80 of all mapped msgls have an azimuth within 5 from the mean values and a fairly constant lateral spacing mode 200 300 m median 330 m which we interpret as an indication that msgls are a spatially self organized phenomenon results show that size shape and spatial arrangement of msgls are consistent both within and also generally between different ice stream beds we suggest this results from a common mechanism of formation which is largely insensitive to local factors although the elongation of msgls mode 6 8 median 12 2 is typically higher than features described as drumlins these values and those of their width mode 100 200 m median 268 m overlap which suggests the two landforms are part of a morphological continuum and may share a similar origin we compare their morphometry with explicit predictions made by the groove ploughing and rilling instability theories of msgl formation although the latter was most compatible neither is fully supported by observations 2014 the authors earth surface processes and landforms published by john wiley sons ltd

carrier phase delay altimetry with gps reflection occultation interferometry from low earth orbiters 1 gps signals reflected off the surface of the earth can be detected by receivers aboard occulting low earth orbiters leos in this work carrier phase interferometry between the reflected and direct occultation signals is performed to infer its relative delay at centimetric error our analysis shows that submeter sensitivity on the surface heights can formally be reached with this technique the potential applications to polar ice altimetry are discussed

seabed corrugations beneath an antarctic ice shelf revealed by autonomous underwater vehicle survey origin and implications for the history of pine island glacier 1 ice shelves are critical features in the debate about west antarctic ice sheet change and sea level rise both because they limit ice discharge and because they are sensitive to change in the surrounding ocean the pine island glacier ice shelf has been thinning rapidly since at least the early 1990s which has caused its trunk to accelerate and retreat although the ice shelf front has remained stable for the past six decades past periods of ice shelf collapse have been inferred from relict seabed corrugations corrugated ridges preserved 340 km from the glacier in pine island trough here we present high resolution bathymetry gathered by an autonomous underwater vehicle operating beneath an antarctic ice shelf which provides evidence of long term change in pine island glacier corrugations and ploughmarks on a sub ice shelf ridge that was a former grounding line closely resemble those observed offshore interpreted previously as the result of iceberg grounding the same interpretation here would indicate a significantly reduced ice shelf extent within the last 11 kyr implying holocene glacier retreat beyond present limits or a past tidewater glacier regime different from today the alternative that corrugations were not formed in open water would question ice shelf collapse events interpreted from the geological record revealing detail of another bed shaping process occurring at glacier margins we assess hypotheses for corrugation formation and suggest periodic grounding of ice shelf keels during glacier unpinning as a viable origin this interpretation requires neither loss of the ice shelf nor glacier retreat and is consistent with a stable grounding line configuration throughout the holocene

the eddy experiment accurate gnss r ocean altimetry from low altitude aircraft 1 during the eddy experiment two synchronous gps receivers were flown at 1 km altitude to collect l1 signals and their reflections from the sea surface for assessment of altimetric precision and accuracy wind speed u10 was around 10 m s and swh up to 2 m a geophysical parametric waveform model was used for retracking and estimation of the lapse between the direct and reflected signals with a 1 second precision of 3 m the lapse was used to estimate the ssh along the track using a differential model the rms error of the 20 km averaged gnss r absolute altimetric solution with respect to jason 1 ssh and a gps buoy measurement was of 10 cm with a 2 cm mean difference multipath and retracking parameter sensitivity due to the low altitude are suspected to have degraded accuracy this result provides an important milestone on the road to a gnss r mesoscale altimetry space mission

bistatic scattering of gps signals off arctic sea ice this paper evaluates the potential of a global positioning system gps bistatic radar for the retrieval of information concerning the presence and condition of sea ice cover for this purpose the permittivity and roughness of a ground scattering target at l band are extracted from reflected gps waveforms collected from an airborne platform using the kirchhoff approximation for the surface cross section the retrieved gps estimates are then evaluated against collocated measurements of surface roughness obtained from a lidar profiler and a reference classification of sea ice types inferred from a multisensor data set that includes polarimetric microwave emissions radarsat backscatter and moderate resolution imaging spectroradiometer infrared visible imagery

sea ice detection using u k tds 1 gnss r data a sea ice detection algorithm developed using the u k techdemosat 1 u k tds 1 global navigation satellite systems gnsss reflectometry data over the arctic and antarctic regions is presented it is based on measuring the similarity of the received gnss reflected waveform or delay doppler map ddm to the coherent reflection model waveform over the open ocean the scattered signal has a diffusive incoherent nature it is described by the rough surface scattering model based on the geometric optics and the gaussian statistics for the ocean surface slopes over sea ice and in particular newly formed sea ice the scattered signal acquires a coherence which is characteristic for a surface with large flat areas in order to measure the similarity of the received waveform or ddm to the coherent reflection model three different estimators are presented the normalized ddm average the trailing edge slope tes and the matched filter approach here a probabilistic study is presented based on a bayesian approach using two different and independent ground truth data sets this approach allows one to thoroughly assess the performance of the estimators the best results are achieved for both the tes and the matched filter approach with a probability of detection of 98 5 a probability of false alarm of 3 6 and a probability of error of 2 5 however the matched filter approach is preferred due to its simplicity data from amsr2 processed using the arctic radiation and turbulence interaction study sea ice algorithm and from an special sensor microwave imager sounder radiometer processed by ocean and sea ice saf have been used as ground truth a pixel has been classified as a sea ice pixel if the sea ice concentration sic in it was larger than 15 the measurement of the sic is also assessed in this paper but the nature of the u k tds 1 data lack of calibrated data does not allow to make any specific conclusions about the sic

first spaceborne observation of sea surface height using gps reflectometry an analysis of spaceborne global positioning system reflectometry gps r data from the techdemosat 1 tds 1 satellite is carried out to image the ocean sea surface height ssh an ssh estimation algorithm is applied to gps r delay waveforms over two regions in the south atlantic and the north pacific estimates made from tds 1 overpasses during a 6 month period are aggregated to produce ssh maps of the two regions the maps generally agree with the global dtu10 mean sea surface height the gps r instrument is designed to make bistatic measurements of radar cross section for ocean wind observations and its altimetric performance is not optimized the differences observed between measured and dtu10 ssh can be attributed to limitations with the gps r instrument and the lack of precision orbit determination by the tds 1 platform these results represent the first observations of ssh by a spaceborne gps r instrument

independent dem of antarctica using gnss r data from techdemosat 1 the first digital elevation model dem of the antarctic ice sheet derived from global navigation satellite systems reflectometry gnss r data from the uk techdemosat 1 satellite is presented this is obtained using 32 months of data from the mission this opportunistic and inexpensive method is shown to produce encouraging results from the technology demonstration platform of techdemosat 1 with median bias under 18 m and root mean square difference under 91 m when compared to the cryosat 2 1 km dem v1 0 discrepancies between the two data sets are explored along with possible causes of such differences and potential improvements to further optimize this technique for future gnss r missions

5 cm precision aircraft ocean altimetry using gps reflections 1 we present the first two aircraft global positioning system gps reflection altimetry measurements the most precise gps ocean altimetry measurement and demonstrate the altimetric precision and spatial resolution necessary to map mesoscale eddies our first experiment demonstrated a 14 cm precision single satellite ocean altimetry measurement while our more recent experiment demonstrates 5 cm altimetric precision with 5 km spatial resolution the new results show significant improvement over our previous effort due to improved modeling greater aircraft altitudes and velocities improved receiver positioning and better experimental control plans to further reduce speckle and refine models to obtain 5 cm altimetric accuracy are presented

first spaceborne phase altimetry over sea ice using techdemosat 1 gnss r signals a track of sea ice reflected global navigation satellite system gnss signal collected by the techdemosat 1 mission is processed to perform phase altimetry over sea ice high precision carrier phase measurements are extracted from coherent gnss reflections at a high angle of elevation 57 the altimetric results show good consistency with a mean sea surface mss model and the root mean square difference is 4 7 cm with an along track sampling distance of 140 m and a spatial resolution of 400 m the difference observed between the altimetric results and the mss shows good correlation with the colocated sea ice thickness data from soil moisture and ocean salinity this is consistent with the reflecting surface aligned with the bottom of the ice water interface due to the penetration of the gnss signal into the sea ice therefore these high precision altimetric results have potential to be used for determination of sea ice thickness

field studies of bottom crevasses in the ross ice shelf antarctica analyse des crevasses observees par sondages radar aeriens et terrestres localisation de leurs points de formation

the paris ocean altimeter in orbit demonstrator mesoscale ocean altimetry remains a challenge in satellite remote sensing conventional nadir looking radar altimeters can make observations only along the satellite ground track and many of them are needed to sample the sea surface at the required spatial and temporal resolutions the passive reflectometry and interferometry system paris using global navigation satellite systems gnss reflected signals was proposed as a means to perform ocean altimetry along several tracks simultaneously spread over a wide swath the bandwidth limitation of the gnss signals and the large ionospheric delay at l band are however issues which deserve careful attention in the design and performance of a paris ocean altimeter this paper describes such an instrument specially conceived to fully exploit the gnss signals for best altimetric performance and to provide multifrequency observations to correct for the ionospheric delay furthermore an in orbit demonstration mission that would prove the expected altimetric accuracy suited for mesoscale ocean science is proposed

penetration depth of interferometric synthetic aperture radar signals in snow and ice digital elevation models of glaciated terrain produced by the nasa jet propulsion laboratory jpl airborne interferometric synthetic aperture radar insar instrument in greenland and alaska at the c 5 6 cm wave length and l band 24 cm frequencies were compared with surface elevation measured from airborne laser altimetry to estimate the phase center of the interferometric depth or penetration depth p on cold polar firn at greenland summit p 9 2m at c and 14 4m at l band on the exposed ice surface of jakobshavn isbrae west greenland p 1 2 m at c and 3 3 m at l band except on smooth marginal ice where p 15 5 m on colder marginal ice of northeast greenland p reaches 60 to 120 m at l band on the temperate ice of brady glacier alaska p is 4 2 m at c and 12 6 m at l band with little dependence on snow ice conditions the implications of the results on the scientific use of insar data over snow ice terrain is discussed

aligned glaciotectonic rafts on the central barents sea seafloor revealing extensive glacitectonic erosion during the last deglaciation 1 erosion rates on glaciated continental shelves are remarkably high especially within ice stream troughs although glaciotectonic erosion may have considerably contributed to enhanced glacial erosion of these landscapes entrainment mechanisms of glaciotectonically emplaced megablocks and rafts remain little understood here we report a northeast southwest trending chain of over 1300 glacial rafts observed on the seafloor in bjornoyrenna a paleo ice stream trough with particularly high erosion rates the landform assemblage adjacent to the glacial rafts includes streamlined bedforms and crevasse squeeze ridges and may represent a lateral shear zone where a paleo ice stream met cold stagnant ice during the last deglaciation individual glacial rafts along the chain are up to 30 m high tend to be elongated with lengths and widths on the order of tens of meters and are oriented from northeast southwest to north south the north southern rearrangement of rafts may reflect a compressional strain regime along the ice stream margin

high resolution sub ice shelf seafloor records of twentieth century ungrounding and retreat of pine island glacier west antarctica pine island glacier ice shelf pigis has been thinning rapidly over recent decades resulting in a progressive drawdown of the inland ice and an upstream migration of the grounding line the resultant ice loss from pine island glacier pig and its neighboring ice streams presently contributes an estimated 10 to global sea level rise motivating efforts to constrain better the rate of future ice retreat one route toward gaining a better understanding of the processes required to underpin physically based projections is provided by examining assemblages of landforms and sediment exposed over recent decades by the ongoing ungrounding of pig here we present high resolution bathymetry and sub bottom profiler data acquired by autonomous underwater vehicle auv surveys beneath pigis in 2009 and 2014 respectively we identify landforms and sediments associated with grounded ice flow proglacial and subglacial sediment transport overprinting of lightly grounded ice shelf keels and stepwise grounding line retreat the location of a submarine ridge jenkins ridge coincides with a transition from exposed crystalline bedrock to abundant sediment cover potentially linked to a thick sedimentary basin extending upstream of the modern grounding line the capability of acquiring high resolution data from auv platforms enables observations of landforms and understanding of processes on a scale that is not possible in standard offshore geophysical surveys