Snow Probe Research Articles

Ground-penetrating radar as a tool for determining the interface between temperate and cold ice, and snow depth: a case study for Hurd-Johnsons glaciers, Livingston Island, Antarctica

Abstract We analyze the internal structure of two polythermal glaciers, Hurd and Johnsons, located on Livingston Island, Antarctica, using 200 and 750 MHz GPR data collected in 2003/04, 2008/09 and 2016/17 field campaigns. Based on the different permittivities of snow and ice, we determined the thickness distribution of the end-of winter snow cover and of the cold ice layer. Their knowledge is fundamental for mass balance and glacier dynamics studies due to the different densities and rheological properties of such media. The average measured thicknesses for the snow and cold ice layers (the latter including the snow layer) were of 1.44 ± 0.09 and 29.1 ± 1.5 m, and their corresponding maxima were of 2.45 ± 0.21 and 80.8 ± 2.5 m. GPR snow profiling allowed for extension of the coverage of the snow thickness survey, but added little information to that supplied by snow pits, stake readings and manual snow probing, because of the multiplicity of reflections within the seasonal snowpack caused by internal ice layers and lenses. The polythermal structure determined for Hurd Glacier fits into the so-called Scandinavian type, seldom reported for the Antarctic region.

Can Weather Radars Be Used to Estimate Snow Accumulation on Alpine Glaciers? An Evaluation Based on Glaciological Surveys

AbstractThe snow water equivalent (SWE) is a key component for understanding changes in the cryosphere in high mountain regions. Yet, a reliable quantification at a high spatiotemporal resolution remains challenging in such environments. In this study, we investigate the potential of an operational weather radar–rain gauge composite (CombiPrecip) to infer the daily evolution of SWE on seven Swiss glaciers. To this end, we validate cumulative CombiPrecip estimates with glacier-wide manual SWE observations (snow probing, snow pits) obtained around the time of the seasonal peak during four winter seasons (2015–19). CombiPrecip underestimates the end-of-season snow accumulation by factors of 2.2 up to 3.7, depending on the glacier site. These factors are consistent over the four winter seasons. The regional variability can be mainly attributed to the empirical visibility of the Swiss radar network within the Alps. To account for the underestimation, we investigate three approaches to adjust CombiPrecip for the applicability to glacier sites. Thereby, we combine the factor of underestimation with a precipitation-phase parameterization. For further comparison, we apply a rain gauge catch-efficiency function based on wind speed. We validate these approaches with 14 manual point observations of SWE obtained on two glaciers during three winter seasons. All approaches show a similar improvement of CombiPrecip estimates. We conclude that CombiPrecip has great potential to estimate SWE on glaciers at a high temporal resolution, but further investigations are necessary to understand the regional variability of the bias throughout the Swiss Alps.

Spatially Extensive Ground‐Penetrating Radar Snow Depth Observations During NASA's 2017 SnowEx Campaign: Comparison With In Situ, Airborne, and Satellite Observations

AbstractSeasonal snow is an important component of Earth's hydrologic cycle and climate system, yet it remains challenging to consistently and accurately measure snow depth and snow water equivalent (SWE) across the range of diverse snowpack conditions that exist on Earth. The NASA SnowEx campaign is focused on addressing the primary gaps in snow remote sensing in order to gain an improved spatiotemporal understanding of this important resource and to further efforts toward a future satellite‐based snow remote sensing mission. Ground‐penetrating radar (GPR) is an efficient and mature approach for measuring snow depth and SWE. We collected ~1.3 million GPR snow depth observations during the NASA SnowEx 2017 campaign, yielding a spatially extensive (~133‐km total length) and high‐resolution (~10‐cm lateral spacing) validation data set to assess various remote sensing and modeling approaches. We found high correlation between the GPR and manual snow probe derived snow depths (r = 0.89, p < 0.0001, root‐mean‐square error (RMSE) = 18 cm), but a median difference of −10 cm, which we attribute, in part, to probe penetration into the unfrozen subsurface. We also compared GPR‐derived snow depths to two other independent estimates of snow depth, as an example of how this data set can be used for validation of remote sensing techniques: Airborne Snow Observatory lidar‐derived snow depths (r = 0.90, p < 0.0001, median difference = −1 cm, RMSE = 14 cm) and preliminary DigitalGlobe WorldView‐3 satellite‐derived snow depths (r = 0.70, p < 0.0001, median difference = −3 cm, RMSE = 24 cm).

A compilation of multitemporal TLS snow depth distribution maps at the Weisssee snow research site (Kaunertal, Austria)

AbstractThe study presents a data set of the interannual and intraannual snow depth distribution recorded by terrestrial laser scanning (TLS) scans at Weisssee snow research site in Austria between November 2014 and May 2018. The data set comprises 23 snow‐on digital elevation models, one snow‐off digital elevation model, and the difference raster calculated between a snow‐off and snow‐on scans. The relative accuracy of the TLS scans was determined by measuring the distance between snow‐free planes from the snow‐on and snow‐off scans and shows mean values smaller than 0.03 m and standard deviations ranging between 0.02 and 0.1 m. The reliability of the snow depths derived from TLS was further assessed by comparing snow depths from snow probing, Global Navigation Satellite System measurements, and continuous snow depth measurements from the weather station. Comparison of the different measurement methods shows average deviations of less than 0.1 m. The data can be used for analysis and modeling of snow distribution or for assessing the representativeness of snow sensors or other remote sensing products.

Repeat mapping of snow depth across an alpine catchment with RPAS photogrammetry

Abstract. Being dynamic in time and space, seasonal snow represents a difficult target for ongoing in situ measurement and characterisation. Improved understanding and modelling of the seasonal snowpack requires mapping snow depth at fine spatial resolution. The potential of remotely piloted aircraft system (RPAS) photogrammetry to resolve spatial variability of snow depth is evaluated within an alpine catchment of the Pisa Range, New Zealand. Digital surface models (DSMs) at 0.15 m spatial resolution in autumn (snow-free reference) winter (2 August 2016) and spring (10 September 2016) allowed mapping of snow depth via DSM differencing. The consistency and accuracy of the RPAS-derived surface was assessed by the propagation of check point residuals from the aero-triangulation of constituent DSMs and via comparison of snow-free regions of the spring and autumn DSMs. The accuracy of RPAS-derived snow depth was validated with in situ snow probe measurements. Results for snow-free areas between DSMs acquired in autumn and spring demonstrate repeatability yet also reveal that elevation errors follow a distribution that substantially departs from a normal distribution, symptomatic of the influence of DSM co-registration and terrain characteristics on vertical uncertainty. Error propagation saw snow depth mapped with an accuracy of ±0.08 m (90 % c.l.). This is lower than the characterization of uncertainties on snow-free areas (±0.14 m). Comparisons between RPAS and in situ snow depth measurements confirm this level of performance of RPAS photogrammetry while also highlighting the influence of vegetation on snow depth uncertainty and bias. Semi-variogram analysis revealed that the RPAS outperformed systematic in situ measurements in resolving fine-scale spatial variability. Despite limitations accompanying RPAS photogrammetry, which are relevant to similar applications of surface and volume change analysis, this study demonstrates a repeatable means of accurately mapping snow depth for an entire, yet relatively small, hydrological catchment (∼0.4 km2) at very high resolution. Resolving snowpack features associated with redistribution and preferential accumulation and ablation, snow depth maps provide geostatistically robust insights into seasonal snow processes, with unprecedented detail. Such data will enhance understanding of physical processes controlling spatial distributions of seasonal snow and their relative importance on varying spatial and temporal scales.

Thin Sea Ice, Thick Snow, and Widespread Negative Freeboard Observed During N‐ICE2015 North of Svalbard

AbstractIn recent years, sea‐ice conditions in the Arctic Ocean changed substantially toward a younger and thinner sea‐ice cover. To capture the scope of these changes and identify the differences between individual regions, in situ observations from expeditions are a valuable data source. We present a continuous time series of in situ measurements from the N‐ICE2015 expedition from January to June 2015 in the Arctic Basin north of Svalbard, comprising snow buoy and ice mass balance buoy data and local and regional data gained from electromagnetic induction (EM) surveys and snow probe measurements from four distinct drifts. The observed mean snow depth of 0.53 m for April to early June is 73% above the average value of 0.30 m from historical and recent observations in this region, covering the years 1955–2017. The modal total ice and snow thicknesses, of 1.6 and 1.7 m measured with ground‐based EM and airborne EM measurements in April, May, and June 2015, respectively, lie below the values ranging from 1.8 to 2.7 m, reported in historical observations from the same region and time of year. The thick snow cover slows thermodynamic growth of the underlying sea ice. In combination with a thin sea‐ice cover this leads to an imbalance between snow and ice thickness, which causes widespread negative freeboard with subsequent flooding and a potential for snow‐ice formation. With certainty, 29% of randomly located drill holes on level ice had negative freeboard.

Application of Low-Cost UASs and Digital Photogrammetry for High-Resolution Snow Depth Mapping in the Arctic

The repeat acquisition of high-resolution snow depth measurements has important research and civil applications in the Arctic. Currently the surveying methods for capturing the high spatial and temporal variability of the snowpack are expensive, in particular for small areal extents. An alternative methodology based on Unmanned Aerial Systems (UASs) and digital photogrammetry was tested over varying surveying conditions in the Arctic employing two diverse and low-cost UAS-camera combinations (500 and 1700 USD, respectively). Six areas, two in Svalbard and four in Greenland, were mapped covering from 1386 to 38,410 m2. The sites presented diverse snow surface types, underlying topography and light conditions in order to test the method under potentially limiting conditions. The resulting snow depth maps achieved spatial resolutions between 0.06 and 0.09 m. The average difference between UAS-estimated and measured snow depth, checked with conventional snow probing, ranged from 0.015 to 0.16 m. The impact of image pre-processing was explored, improving point cloud density and accuracy for different image qualities and snow/light conditions. Our UAS photogrammetry results are expected to be scalable to larger areal extents. While further validation is needed, with the inclusion of extra validation points, the study showcases the potential of this cost-effective methodology for high-resolution monitoring of snow dynamics in the Arctic and beyond.

小型無人航空機（UAV）を用いた積雪深分布の推定と検証

小型無人航空機（UAV）を用いた積雪深分布の推定と検証

Observaciones del manto de nieve durante una circunnavegación del casquete de hielo de Groenlandia (primavera de 2014)

Este trabajo describe las características del manto de nieve de Groenlandia a partir de datos recogidos durante la circunnavegación del casquete de hielo de Groenlandia durante la primavera de 2014. La base de datos incluye medidas de espesor de nieve en parcelas de 100 m2, y datos de densidad y de temperatura del manto de nieve a un metro de profundidad medido en 25 puntos a lo largo del trayecto de 4301 kilómetros realizados durante 49 días. Además, se midió la temperatura y densidad de la nieve a intervalos de 10 centímetros en ocho perfiles de un metro de profundidad. Esta información puede resultar de interés para el estudio del manto de nieve en está remota región, así como proporcionar información de utilidad para modelizadores de la atmósfera y procesos criosféricos.El espesor de nieve excedió con frecuencia los 4 metros de profundidad, si bien no se pudo superar en ocasiones una capa de hielo localizada aproximadamente a 70 centímetros de profundidad. Esta capa de hielo está posiblemente asociada al evento de fusión de julio de 2012 que afectó a un 98% de la superficie del casquete de hielo. Fuera de la zona de acumulación, el espesor de nieve medido fue bastante constante en torno a 1.5 metros. La temperatura del manto de nieve osciló entre los -20º y -10ºC en la mayor parte de los casos, y ha mostrado una correlación muy alta con la temperatura del aire de los 15 días anteriores a la medida. La densidad del manto de nieve fue bastante homogénea en la mayoría de los puntos de medición, oscilando entre los 320 to 390 kg m–3. Los perfiles de temperatura y densidad informan de un manto de nieve progresivamente más frío en las capas más profundas, observándose los mayores (menores) gradientes en las zonas más cálidas (frías). Se detecta un tramo de mayor densidad en torno a los 60-80 cm, coincidiendo con la capa de hielo previamente detectada. En las zonas menos frías del recorrido, se ha encontrado una capa más densa relativamente próxima a la superficie, posiblemente debida a un evento de fusión más reciente.

Device with rectangular section for layer-by-layer snow sampling

A new snow layer probing device with a rectangular section is described in the paper. This device allows receiving snow samples with the undisturbed structures of snow layers, and more accurately reflects the actual value of the snow water equivalent. Application of a new snow probing device in snow measurements provides a new way to organize the monitoring dynamics of snow density layer variability, to estimate density of certain snow types in the snow cover, including the total or vertically averaged one, and to visualize the features of the snow stratigraphy structure. Snow layer probing device with a rectangular section as opposed to the cylindrical weight snow devices has constructive advantages. It also can be used in the calibration weight snow measurement devices that will ensure the comparability of the snow shooting results made in different climatic zones.

The Clacton Spear: The Last One Hundred Years

In 1911, an eminent amateur prehistorian pulled the broken end of a pointed wooden shaft from Palaeolithic-age sediments at a seaside town in Essex. This artefact, still the earliest worked wood to be discovered in the world, became known as the Clacton spear. Over the past one hundred years it has variously been interpreted as a projectile weapon, a stave, a digging stick, a snow probe, a lance, a game stake and a prod to ward off rival scavengers. These perspectives have followed academic fashions and as the popular views of early hominins have altered. Since discovery, the Clacton spear has also been replicated twice, has undergone physical transformations due to preservation treatments, and has featured in two public exhibitions. Within this article the changing context of the spear, its parallels, and all previous conservation treatments and their impacts are assessed.

Gin Flat Snow Water Equivalent Estimation from Field Methods

Snow surveying is an engineering ground inventory procedure that collects snow water equivalent (SWE) measurements, depths of snow, and snow densities. The ability to successfully acquire these measurements accurately allows for an estimate in the amount of water available. We used methods of snow probing, snow coring, and the use of snow pits to nd the SWE and density at dierent lo

A comparison of measurement methods: terrestrial laser scanning, tachymetry and snow probing for the determination of the spatial snow-depth distribution on slopes

AbstractDetermination of the spatial snow-depth distribution is important in potential avalanche-starting zones, both for avalanche prediction and for the dimensioning of permanent protection measures. Knowledge of the spatial distribution of snow is needed in order to validate snow depths computed from snowpack and snowdrift models. The inaccessibility of alpine terrain and the acute danger of avalanches complicate snow-depth measurements (e.g. when probes are used), so the possibility of measuring the snowpack using terrestrial laser scanning (TLS) was tested. The results obtained were compared to those of tachymetry and manual snow probing. Laser measurements were taken using the long-range laser profile measuring system Riegl LPM-i800HA. The wavelength used by the laser was 0.9 μm (near-infrared). The accuracy was typically within 30 mm. The highest point resolution was 30 mm when measured from a distance of 100 m. Tachymetry measurements were carried out using Leica TCRP1201 systems. Snowpack depths measured by the tachymeter were also used. The datasets captured by tachymetry were used as reference models to compare the three different methods (TLS, tachymetry and snow probing). This is the first time that the accuracy of TLS systems in snowy and alpine weather conditions has been quantified. The relative accuracy between the three measurement methods is bounded by a maximum offset of ±8 cm. Between TLS and the tachymeter the standard deviation is 1σ = 2 cm, and between manual probing and TLS it is up to 1σ = 10 cm, for maximum distances for the TLS and tachymeter of 300 m.

Measurement of snow dielectric constant profile at UHF band using probe sensor array

AbstractIn this paper, with regard to a resonant sensor of a three‐parallel line type consisting of a snow probe sensor array placed in snow for long‐term measurement of the complex permittivity profile of accumulated snow layers at UHF frequencies, a derivation of an approximate formula for estimating the constant permittivity on the basis of the method of moments and experimental verification results are presented. The measured snow dielectric constant profile over a period of about 2 weeks at Aomori Airport is described. In particular, the change from dry snow to wet snow associated with snow melting is acquired. Hence, the effectiveness of the probe sensor for long‐term measurement of the snow dielectric constant is confirmed. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(4): 10–19, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20186

A mean net accumulation pattern derived from radioactive layers and radar soundings on Austfonna, Nordaustlandet, Svalbard

AbstractWe present the snow-accumulation distribution over Austfonna, Nordaustlandet, Svalbard, based on 29 shallow ice cores that were retrieved from this ice cap during 1998 and 1999. Mean annual net accumulation is deduced from radioactive layers resulting from the 1954–74 atmospheric nuclear tests (maximum in 1963) and the Chernobyl accident (1986). The Chernobyl layer was located in 19 ice cores in the accumulation area, and the nuclear test layer was located in two deeper ice cores. In addition, the spatial variation of the depth of winter 1998/99 snowpack was mapped using snow probing, ground-penetrating radar methods and pit studies. The altitudinal gradient of the mean annual net mass balance and the altitude of the mean equilibrium line are determined along five transects ending at the top of the ice cap. The mean annual net mass balance and the equilibrium-line altitudes show a high degree of asymmetry between the western and eastern parts of Austfonna, in accordance with the distribution of winter accumulation. Large interannual variations of the accumulation exist. However, the study of the mean annual net mass balance shows no trend for two different time periods, 1963–86 and 1986 to the date of the drillings (1998/99).

Effect of uncertainties in measured variables on the calculated mass balance of storglaciären

Detailed mass balance measurements have been carried out on Storglaciären since 1945, adhering to a fixed system of measurements since the 1960s. Using a geographical information system approach, the effect of parameters such as density conversion model, systematic snow probing error and ablation gradient calculation on the mass balance of the glacier can be investigated. It is evident that the measure of total mass balance of Storglaciären is not sensitive to variations in these parameters. This means that reasonable estimates of the mass balance of a glacier can be made with very little information, given that measurements are distributed over the glacier surface. However, the uncertainty that may result from varying the parameters is c. 0.1 m water equivalent. Hence, reporting mass balance to centimetre or even millimetre resolution is questionable. When considering mass balance measurements as input for flow models, for example, i.e. requiring a distributed balance, the detail necessary in the measurements becomes significantly greater. At this level careful attention must be made to all parameters entering the mass balance calculation. From this it seems evident that any measurements at intermediate complexity do not increase the accuracy of the mass balance in relation to the extra work required and that the choice of method determines the scientific problems to which the data is applicable.

Scanning near-field optical microscopy using piezoelectric cantilevers

Microfabricated cantilevers for atomic force microscopy (AFM), used as scanning near-field optical microscopy (SNOM) probes, have remarkable advantages because the fabrication process is well established. In addition, the SNOM probe can be combined with an atomic fore microscope, which is capable of detecting various surface properties. However, the optical method for measuring the deflection of the cantilever often disturbs the detection of weak evanescent light. We have developed a new SNOM probe using a microfabricated cantilever with a piezoelectric thin film as an integrated deflection sensor so that any optical measurements for the deflection are not required. The cantilever is made of Si with deposited layers of Pt/lead ziconate titanate (PZT)/Pt and an SiN hollow pyramidal tip at the en The light scattered by the tip can transmit the cantilever when the PZT cantilever is brought in close proximity to a sample surface. The tip-to-sample distance is regulated using the piezoelectric current while the cantilever is vibrated at its resonance frequency. Both topographic and optical images were obtained successfully by the new SNOW probe.

Using ground-penetrating radar to image previous years’ summer surfaces for mass-balance measurements

In traditional mass-balance measurements one estimates winter snow accumulation by identifying the depth to the previous summer’s snow or ice surface using a snow probe. This is labor-intensive and unreliable for inhomogeneous summer surfaces. Another method is to image internal reflection horizons using a ground-penetrating radar (GPR), which has advantages in speed and areal coverage over traditional probing. However, to obtain quantitative mass-balance measurements from GPR images one needs to convert the time scale to a depth scale, not a straightforward problem. We compare a GPR section with dielectric profiles and visual stratigraphy of three snow cores, manual probings, and previous mass-balance measurements. We relate changes in snow-core dielectric properties to changes in density and to the travel times of reflecting horizons in the GPR section, and correlate some of these reflecting horizons with previous summer surfaces. We conclude that GPR can be used as a complementary tool in mass-balance measurements, giving a wide areal survey of winter accumulation and net balance for preceding years. However, proper calibration is essential for identifying specific surfaces in the radar data.

Using ground-penetrating radar to image previous years’ summer surfaces for mass-balance measurements

In traditional mass-balance measurements one estimates winter snow accumulation by identifying the depth to the previous summer’s snow or ice surface using a snow probe. This is labor-intensive and unreliable for inhomogeneous summer surfaces. Another method is to image internal reflection horizons using a ground-penetrating radar (GPR), which has advantages in speed and areal coverage over traditional probing. However, to obtain quantitative mass-balance measurements from GPR images one needs to convert the time scale to a depth scale, not a straightforward problem. We compare a GPR section with dielectric profiles and visual stratigraphy of three snow cores, manual probings, and previous mass-balance measurements. We relate changes in snow-core dielectric properties to changes in density and to the travel times of reflecting horizons in the GPR section, and correlate some of these reflecting horizons with previous summer surfaces. We conclude that GPR can be used as a complementary tool in mass-balance measurements, giving a wide areal survey of winter accumulation and net balance for preceding years. However, proper calibration is essential for identifying specific surfaces in the radar data.

Snow probe for in situ determination of wetness and density

The amount of water present in liquid form in a snowpack exercises a strong influence on the radar and radiometric responses of snow. Conventional techniques for measuring the liquid water content m/sub /spl upsi// suffer from various shortcomings, which include poor accuracy, long analysis time, poor spatial resolution, and/or cumbersome and inconvenient procedures. This paper describes the development of a hand-held electromagnetic sensor for quick and easy determination of snow liquid water content and density. A novel design of this probe affords several important advantages over existing similar sensors. Among these are improved spatial resolution and accuracy, and reduced sensitivity to interference by objects or media outside the sample volume of the sensor. The sensor actually measures the complex dielectric constant of the snow medium, and the water content and density must be obtained through the use of empirical or semi-empirical relations. To test the suitability of existing models and allow the development of new models, the snow probe was tested against the freezing calorimeter and gravimetric density determinations. From these comparisons, valid models were selected or developed. Based on the use of these models, the following specifications were established for the snow probe: 1) liquid water content measurement accuracy=/spl plusmn/0.66% in the wetness range from 0 to 10% by volume and 2) wet snow density measurement accuracy=/spl plusmn/0.05 g/cm/sup 3/ in the density range from 0.1 to 0.6 g/cm/sup 3/. >