scholarly journals Correcting for Systematic Underestimation of Topographic Glacier Aerodynamic Roughness Values From Hintereisferner, Austria

2021 ◽  
Vol 9 ◽  
Author(s):  
Joshua R. Chambers ◽  
Mark W. Smith ◽  
Thomas Smith ◽  
Rudolf Sailer ◽  
Duncan J. Quincey ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Regional Scale ◽  
Laser Scanner ◽  
Turbulent Energy ◽  
Temporal Variations ◽  
Glacier Surface ◽  
Order Of Magnitude ◽  
Spatio Temporal ◽  
Aerodynamic Roughness ◽  
Elevation Model

Spatially-distributed values of glacier aerodynamic roughness (z0) are vital for robust estimates of turbulent energy fluxes and ice and snow melt. Microtopographic data allow rapid estimates of z0 over discrete plot-scale areas, but are sensitive to data scale and resolution. Here, we use an extensive multi-scale dataset from Hintereisferner, Austria, to develop a correction factor to derive z0 values from coarse resolution (up to 30 m) topographic data that are more commonly available over larger areas. Resulting z0 estimates are within an order of magnitude of previously validated, plot-scale estimates and aerodynamic values. The method is developed and tested using plot-scale microtopography data generated by structure from motion photogrammetry combined with glacier-scale data acquired by a permanent in-situ terrestrial laser scanner. Finally, we demonstrate the application of the method to a regional-scale digital elevation model acquired by airborne laser scanning. Our workflow opens up the possibility of including spatio-temporal variations of z0 within glacier surface energy balance models without the need for extensive additional field data collection.

scholarly journals Small-scale spatio-temporal characteristics of accumulation rates in western Dronning Maud Land, Antarctica

2008 ◽  
Vol 54 (185) ◽  
pp. 315-323 ◽  
Author(s):  
Helgard Anschütz ◽  
Daniel Steinhage ◽  
Olaf Eisen ◽  
Hans Oerter ◽  
Martin Horwath ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Temporal Variations ◽  
Spatial Variations ◽  
Small Scale ◽  
Accumulation Rates ◽  
Order Of Magnitude ◽  
Dronning Maud Land ◽  
Spatio Temporal ◽  
Ground Penetrating ◽  
Firn Core

AbstractSpatio-temporal variations of the recently determined accumulation rate are investigated using ground-penetrating radar (GPR) measurements and firn-core studies. The study area is located on Ritscherflya in western Dronning Maud Land, Antarctica, at an elevation range 1400–1560 m. Accumulation rates are derived from internal reflection horizons (IRHs), tracked with GPR, which are connected to a dated firn core. GPR-derived internal layer depths show small relief along a 22 km profile on an ice flowline. Average accumulation rates are about 190 kg m−2 a−1 (1980–2005) with spatial variability (1σ) of 5% along the GPR profile. The interannual variability obtained from four dated firn cores is one order of magnitude higher, showing 1σ standard deviations around 30%. Mean temporal variations of GPRderived accumulation rates are of the same magnitude or even higher than spatial variations. Temporal differences between 1980–90 and 1990–2005, obtained from two dated IRHs along the GPR profile, indicate temporally non-stationary processes, linked to spatial variations. Comparison with similarly obtained accumulation data from another coastal area in central Dronning Maud Land confirms this observation. Our results contribute to understanding spatio-temporal variations of the accumulation processes, necessary for the validation of satellite data (e.g. altimetry studies and gravity missions such as Gravity Recovery and Climate Experiment (GRACE)).

scholarly journals Spatio-Temporal Variations in Foredune Dynamics Determined with Mobile Laser Scanning

2018 ◽  
Vol 6 (4) ◽  
pp. 126 ◽  
Author(s):  
Jasper Donker ◽  
Marcel van Maarseveen ◽  
Gerben Ruessink
Keyword(s):  
Volume Change ◽  
Laser Scanning ◽  
Storm Surges ◽  
Temporal Variations ◽  
Airborne Lidar ◽  
Aeolian Transport ◽  
Sand Surface ◽  
Waves And Currents ◽  
Spatio Temporal ◽  
Rtk Gps

Coastal foredunes are highly dynamic landforms because of rapid erosion by waves and currents during storm surges in combination with gradual accretion by aeolian transport during more quiescent conditions. While our knowledge into the mechanisms behind foredune erosion have reached considerable maturity, this is not the case for foredune growth. High resolution spatio-temporal data sets of beach and foredune topography, which are needed to increase our understanding of mechanisms behind aeolian transport in coastal environments and to develop predictive dune-accretion models, are scarce. Here we aim to illustrate that repeated Mobile Laser Scanning (MLS) surveys provide an accurate and robust method to study detailed changes in dune volume on the timescales of months to years. An MLS system attached to an inertial navigation system with RTK-GPS (INS-GPS) was used to carry out 13 surveys along a 3.5-km Dutch beach over a 2.5-year period. The height observations were post-processed and averaged into 1 × 1 m Digital Elevation Models (DEMs). Comparison with airborne LiDAR and RTK-GPS data revealed that the obtained DEMs were accurate and robust up to a height of 15 m in the foredune above which dense vegetation hampers the MLS to see the sand surface. Estimates of dune volume change of the lower 13 m of the foredune have an uncertainty of about 0.25 m 3 /m. Time series of dune volume change show that at our study site the foredune accretes throughout the year at similar rates (10 m 3 /m/year), while marine erosion is obviously confined to storm surges. Foredune accretion and erosion vary spatially, which can, in part, be related to variations in beach width.

scholarly journals Investigations on intra-annual elevation changes using multi-temporal airborne laser scanning data: case study Engabreen, Norway

2005 ◽  
Vol 42 ◽  
pp. 195-201 ◽  
Author(s):  
Thomas Geist ◽  
Hallgeir Elvehøy ◽  
Miriam Jackson ◽  
Johann Stötter
Keyword(s):  
Mass Balance ◽  
Laser Scanning ◽  
Laser Scanner ◽  
Remote Sensing Data ◽  
Control Area ◽  
Airborne Laser Scanning ◽  
Time Interval ◽  
Scanner Data ◽  
Glacier Surface ◽  
Airborne Laser

AbstractKey issues of glacier monitoring are changes in glacier geometry and glacier mass. As accurate direct measurements are costly and time-consuming, the use of various remote-sensing data for glacier monitoring is explored. One technology used and described here is airborne laser scanning. The method enables the derivation of high-quality digital elevation models (DEMs) with a vertical and horizontal accuracy in the sub-metre range. Between September 2001 and August 2002, three laser scanner data acquisition flights were carried out, covering the whole area of Engabreen, Norway, and corresponding well to the measurement dates for the mass-balance year 2001/02. The data quality of the DEMs is assessed (e.g. by comparing the values with a control area which has been surveyed independently or GPS ground profiles measured during the flights). For the whole glacier, surface elevation change and consequently volume change is calculated, quantified and compared with traditional mass-balance data for the same time interval. For the winter term, emergence/submergence velocity is determined from laser scanner data and snow-depth data and is compared with velocity measurements at stakes. The investigations reveal the high potential of airborne laser scanning for measuring the extent and the topography of glaciers as well as changes in geometry (Δarea, Δvolume).

scholarly journals An improved sea ice detection algorithm using MODIS: application as a new European sea ice extent indicator

2021 ◽  
Vol 15 (6) ◽  
pp. 2803-2818
Author(s):  
Joan Antoni Parera-Portell ◽  
Raquel Ubach ◽  
Charles Gignac
Keyword(s):  
Sea Ice ◽  
Regional Scale ◽  
Ice Cover ◽  
Detection Algorithm ◽  
Temporal Variations ◽  
The Arctic ◽  
Sea Ice Extent ◽  
Monitoring Tools ◽  
Spatio Temporal ◽  
Ice Detection

Abstract. The continued loss of sea ice in the Northern Hemisphere due to global warming poses a threat to biota and human activities, evidencing the necessity of efficient sea ice monitoring tools. Aiming at the creation of an improved sea ice extent indicator covering the European regional seas, the new IceMap500 algorithm has been developed to classify sea ice and water at a resolution of 500 m at nadir. IceMap500 features a classification strategy built upon previous MODIS sea ice extent algorithms and a new method to reclassify areas affected by resolution-breaking features inherited from the MODIS cloud mask. This approach results in an enlargement of mapped area, a reduction of potential error sources and a better delineation of the sea ice edge, while still systematically achieving accuracies above 90 %, as obtained by manual validation. Swath maps have been aggregated at a monthly scale to obtain sea ice extent with a method that is sensitive to spatio-temporal variations in the sea ice cover and that can be used as an additional error filter. The resulting dataset, covering the months of maximum and minimum sea ice extent (i.e. March and September) over 2 decades (from 2000 to 2019), demonstrates the algorithm's applicability as a monitoring tool and as an indicator, illustrating the sea ice decline at a regional scale. The European sea regions located in the Arctic, NE Atlantic and Barents seas display clear negative trends in both March (−27.98 ± 6.01 × 103 km2yr−1) and September (−16.47 ± 5.66 × 103 km2yr−1). Such trends indicate that the sea ice cover is shrinking at a rate of ∼ 9 % and ∼ 13 % per decade, respectively, even though the sea ice extent loss is comparatively ∼ 70 % greater in March.

scholarly journals Fusion of high resolution remote sensing images and terrestrial laser scanning for improved biomass estimation of maize

2014 ◽  
Vol XL-7 ◽  
pp. 101-108 ◽  
Author(s):  
C. Hütt ◽  
H. Schiedung ◽  
N. Tilly ◽  
G. Bareth
Keyword(s):  
High Resolution ◽  
Laser Scanning ◽  
Laser Scanner ◽  
Terrestrial Laser Scanning ◽  
Point Clouds ◽  
Satellite System ◽  
Biomass Estimation ◽  
Digital Elevation ◽  
Elevation Model ◽  
In The Beginning

In this study, images from the satellite system WorldView-2 in combination with terrestrial laser scanning (TLS) over a maize field in Germany are investigated. Simultaneously to the measurements a biomass field campaigns was carried out. From the point clouds of the terrestrial laser scanning campaigns crop surface models (CSM) from each scanning date were calculate to model plant growth over time. These results were resampled to match the spatial resolution of the WorldView-2 images, which had to orthorectified using a high resolution digital elevation model and atmosphere corrected using the ATCOR Software package. A high direct correlation of the NDVI calculated from the WorldView-2 sensor and the dry biomass was found in the beginning of June. At the same date, the heights from laser scanning can also explain a certain amount of the biomass variation (<i>r</i><sup>2</sup> = 0.6). By combining the NDVI from WorldView-2 and the height from the laser scanner with a linear model, the R2 reaches higher values of 0.86. To further understand the relationship between CSM derived crop heights and reflection indices, a comparison on a pixel basis was performed. Interestingly, the correlation of the NDVI and the crop height is rather low at the beginning of June (<i>r</i><sup>2</sup> = 0,4, <i>n</i> = 1857) and increases significantly (<i>R</i><sup>2</sup> = 0,79, <i>N</i> = 1857) at a later stage.

scholarly journals Small-Scale Strain Measurements on a Glacier Surface

1971 ◽  
Vol 10 (59) ◽  
pp. 237-243 ◽  
Author(s):  
S. C. Colbeck ◽  
R. J. Evans
Keyword(s):  
Lower Limit ◽  
Large Scale ◽  
Temporal Variations ◽  
Small Scale ◽  
Flow Conditions ◽  
Glacier Surface ◽  
Strain Measurements ◽  
Order Of Magnitude ◽  
Scale Surface ◽  
Deformation Measurements

AbstractSurface deformations in the neighborhood of a crevasse field were measured over short (3 m) gage lengths in order to study flow conditions associated with crevasse formation. The results obtained were unusual in that they were inconsistent with large-scale results found by previous workers. It was concluded that the presence of small-scale surface effects, such as fractures, pot-holes and healed crevasses give rise to small-scale deformation fields with large spatial and temporal variations and that there is a lower limit of gage length below which deformation measurements pertinent to regional (low phenomena cannot be made. This lower limit is apparently an order of magnitude greater than the spacing of the features which give rise to localized effects.

Imaging the spatio-temporal variations in deep tremor activity using cluster analysis techniques

2021 ◽  
Author(s):  
Anca Opris ◽  
Sumanta Kundu ◽  
Takahiro Hatano
Keyword(s):  
Machine Learning ◽  
Cluster Analysis ◽  
Regional Scale ◽  
Temporal Variations ◽  
Machine Learning Algorithms ◽  
Temporal Behaviour ◽  
Slow Earthquakes ◽  
Short Period ◽  
Spatial Correlation Structure ◽  
Spatio Temporal

&lt;div&gt;More than 15 years of seismic observations on slow earthquakes are available for the Nankai and Cascadia regions, due to the high density of seismic stations and constant improvements. It was observed that deep tremor activity exhibits highly non-Poissonian behaviour, consisting of short-period bursts separated by long periods of inactivity, as well as significant spatial variations throughout a tectonic region (Obara, 2011). Tremor activity in these regions has shown episodic behaviour with different recurrence interval. Modelling the space-time variations can help the unified understanding of the phenomenon. Catalogues with more than 30.000 (Idehara et al., 2014) and 130000 LFE&amp;#8217;s (Mizuno et al, 2019) are available for the world tremor databese. If we consider LFE&amp;#8217;s source as a spatial correlation structure which is evolving in time, in order to reveal the characteristics of this structure, we used the Grassberger Procaccia algorithm to calculate the combined correlation dimension (Tosi et al.,2008) of tremor activity (Cc (r, &amp;#964;)), at both local and regional scale. The integral representation is shown as contour map (facilitating the possibility of using machine learning algorithms based on image processing for identifying the characteristic image of each tremor patch). Thus, implementing machine learning methods for LFE cluster analysis is required. After performing the cluster analysis, we could identify the specific spatio-temporal behaviour of each of the tremor patches in the studied regions, not just the features which were described in previous studies, such as recurrence intervals for short-term slow slip events (Idehara et al., 2014), tremor migration (for monitoring purposes), but also new features which could be used for forecasting.&lt;/div&gt;&lt;div&gt;&amp;#160;&lt;/div&gt;&lt;div&gt;&lt;img src=&quot;https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.0b8b5af57a0068928921161/sdaolpUECMynit/12UGE&amp;app=m&amp;a=0&amp;c=4087202a58071c68d39e6d5f305ba0b4&amp;ct=x&amp;pn=gepj.elif&amp;d=1&quot; alt=&quot;&quot;&gt;&lt;/div&gt;

Implications of methane emissions in biogeochemical budgeting: A study from a eutrophic tropical lake of South India

2020 ◽  
Author(s):  
Revathy Das ◽  
Appukuttan Pillai Krishnakumar ◽  
Krishnan AnoopKrishnan ◽  
Vivekanandan Nandakumar
Keyword(s):  
Plant Biomass ◽  
Regional Scale ◽  
Temporal Variations ◽  
Physical Factors ◽  
Growing Seasons ◽  
Littoral Zones ◽  
Flux Measurements ◽  
The Mean ◽  
Spatio Temporal ◽  
Lake Systems

&lt;p&gt;Greenhouse gases (GHGs), especially, methane (CH&lt;sub&gt;4&lt;/sub&gt;) emissions from the littoral zones of the lakes play an important role in regional biogeochemical budgets. Only a few studies are available in literature highlighting the direct flux measurements of CH&lt;sub&gt;4 &amp;#160;&amp;#160;&lt;/sub&gt;from the aquatic systems. In the present study, an attempt has been made to quantify the spatio-temporal variations of CH&lt;sub&gt;4&lt;/sub&gt;&amp;#160;efflux and the key physical factors controlling the emission rate, from the vegetated littoral zones of lake Vellayani (5.55Km&lt;sup&gt;2&lt;/sup&gt;), located in the urbanized area of Thiruvananthapuram city, Kerala, South-West India. CH&lt;sub&gt;4&lt;/sub&gt;&amp;#160;efflux were collected from different vegetations in littoral zones, using a static chamber, during the peak growing seasons from March to October in 2016 and further analyses were carried out by using Gas Chromatograph (PE Clarus 500, PerkinElmer, Inc.). The mean efflux rate of CH&lt;sub&gt;4 &amp;#160;&amp;#160;&lt;/sub&gt;from the emergent plant species (Phragmites australis and Typha spp.) was 114.4 mg CH&lt;sub&gt;4&lt;/sub&gt; m&lt;sup&gt;-2&lt;/sup&gt;h&lt;sup&gt;-1&lt;/sup&gt;; while, in the floating leaved species (Nymphaea spp. and Nelumbo Spp.), it &lt;sub&gt;&amp;#160;&amp;#160;&lt;/sub&gt;was &amp;#160;&amp;#160;observed to be 32.6 mgCH&lt;sub&gt;4&lt;/sub&gt; m&lt;sup&gt;-2&lt;/sup&gt;h&lt;sup&gt;-1&lt;/sup&gt;. The results reveal that CH&lt;sub&gt;4&lt;/sub&gt; efflux in the zone of emergent vegetation was significantly higher than the floating-leaved zone indicating the importance of plant biomass and standing water depths for the spatial variations of CH&lt;sub&gt;4 &lt;/sub&gt;efflux. However, no significant temporal variations were noticed in the physical factors during the peak growing seasons. These results indicate that the vegetated littoral zones of lake, especially the emergent plant zones were supersaturated with CH&lt;sub&gt;4&lt;/sub&gt;, facilitating the production of carbon for CH&lt;sub&gt;4&lt;/sub&gt; emission&lt;sub&gt;,&lt;/sub&gt; but also enable the release of CH&lt;sub&gt;4 &lt;/sub&gt;by the diffusion from the intercellular gas lacunas. We conclude that the atmospheric CH&lt;sub&gt;4&lt;/sub&gt; emissions will be affected by the growth of exotic species in the lake systems and may be the reason for enhancing the climate warming in local/regional scale.&lt;/p&gt;

scholarly journals A scale-dependent model to represent changing aerodynamic roughness of ablating glacier ice based on repeat topographic surveys

2020 ◽  
Vol 66 (260) ◽  
pp. 950-964
Author(s):  
Thomas Smith ◽  
Mark W. Smith ◽  
Joshua R. Chambers ◽  
Rudolf Sailer ◽  
Lindsey Nicholson ◽  
...  
Keyword(s):  
Energy Balance ◽  
Laser Scanning ◽  
Glacier Surface ◽  
Mountain Glacier ◽  
Ice Surface ◽  
Glacier Ice ◽  
Consistent Increase ◽  
Aerodynamic Roughness ◽  
Surface Ice ◽  
Time Substitution

AbstractTurbulent fluxes make a substantial and growing contribution to the energy balance of ice surfaces globally, but are poorly constrained owing to challenges in estimating the aerodynamic roughness length (z0). Here, we used structure from motion (SfM) photogrammetry and terrestrial laser scanning (TLS) surveys to make plot-scale 2-D and 3-D microtopographic estimations of z0 and upscale these to map z0 across an ablating mountain glacier. At plot scales, we found spatial variability in z0 estimates of over two orders of magnitude with unpredictable z0 trajectories, even when classified into ice surface types. TLS-derived surface roughness exhibited strong relationships with plot-scale SfM z0 estimates. At the glacier scale, a consistent increase in z0 of ~0.1 mm d−1 was observed. Space-for-time substitution based on time since surface ice was exposed by snow melt confirmed this gradual increase in z0 over 60 d. These measurements permit us to propose a scale-dependent temporal z0 evolution model where unpredictable variability at the plot scale gives way to more predictable changes of z0 at the glacier scale. This model provides a critical step towards deriving spatially and temporally distributed representations of z0 that are currently lacking in the parameterisation of distributed glacier surface energy balance models.

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