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Keywords = Byrd Glacier

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25 pages, 10553 KiB  
Article
Structure-From-Motion Photogrammetry of Antarctic Historical Aerial Photographs in Conjunction with Ground Control Derived from Satellite Data
by Sarah F. Child, Leigh A. Stearns, Luc Girod and Henry H. Brecher
Remote Sens. 2021, 13(1), 21; https://doi.org/10.3390/rs13010021 - 23 Dec 2020
Cited by 14 | Viewed by 4208
Abstract
A longer temporal scale of Antarctic observations is vital to better understanding glacier dynamics and improving ice sheet model projections. One underutilized data source that expands the temporal scale is aerial photography, specifically imagery collected prior to 1990. However, processing Antarctic historical aerial [...] Read more.
A longer temporal scale of Antarctic observations is vital to better understanding glacier dynamics and improving ice sheet model projections. One underutilized data source that expands the temporal scale is aerial photography, specifically imagery collected prior to 1990. However, processing Antarctic historical aerial imagery using modern photogrammetry software is difficult, as it requires precise information about the data collection process and extensive in situ ground control is required. Often, the necessary orientation metadata for older aerial imagery is lost and in situ data collection in regions like Antarctica is extremely difficult to obtain, limiting the use of traditional photogrammetric methods. Here, we test an alternative methodology to generate elevations from historical Antarctic aerial imagery. Instead of relying on pre-existing ground control, we use structure-from-motion photogrammetry techniques to process the imagery with manually derived ground control from high-resolution satellite imagery. This case study is based on vertical aerial image sets collected over Byrd Glacier, East Antarctica in December 1978 and January 1979. Our results are the oldest, highest resolution digital elevation models (DEMs) ever generated for an Antarctic glacier. We use these DEMs to estimate glacier dynamics and show that surface elevation of Byrd Glacier has been constant for the past ∼40 years. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Map of Byrd Glacier with the 1978 and 1979 flight paths. The solid lines represent where aerial images were collected and the dashed lines show where the planes turned around. The direction of ice flow for this figure and all following figures is from left to right of the figure. The background image is a band combination composite of Bands 3, 4, and 5 from Landsat-8 OLI images LC80471192019048LGN00 and LC80471182019048LGN00 (also used for all following figures with maps). The inset map in the upper left corner denotes Byrd Glacier’s location in Antarctica.</p> Full article ">Figure 2
<p>The blue arrows to the left of image CA000400V0126 are highlighting the white stripes caused by a malfunction with the aerial camera’s instrument lighting.</p> Full article ">Figure 3
<p>Workflow for generating DEMs from historical imagery. On the left are the steps for manually extracting ground control points (the software used for coregistering is PyBob) and on the right, the SfM photogrammetry processing of the analog aerial images (the images processed using in MicMac and the point clouds are cleaned with CloudCompare). The orange shapes represent manual procedures; the teal shapes are automated steps.</p> Full article ">Figure 4
<p>Establishing interior orientation: (<b>a</b>) Aerial image CA000900V0085 with the protruding fiducial marks labeled as N, S, W, and E. The blue box is highlighting the E fiducial mark and the callout to the right is an enlargement of that fiducial mark with the background imagery whited out. (<b>b</b>) The process of normalizing the aerial photographs where each image is positioned with the same grid spacing and alignment. By resampling the analog film, a homologous digital image dataset is rendered.</p> Full article ">Figure 5
<p>GPS sites on stable rock locations represented by stars. The violet line located near the middle of the glacier’s trunk is the grounding line estimated from 2013 GPS data and 2017 surface elevations [<a href="#B51-remotesensing-13-00021" class="html-bibr">51</a>]. The methodology for identifying the grounding line is similar to Fricker et al. [<a href="#B52-remotesensing-13-00021" class="html-bibr">52</a>] and Brunt et al. [<a href="#B53-remotesensing-13-00021" class="html-bibr">53</a>].</p> Full article ">Figure 6
<p>SfM photogrammetry DEM results for the 1978 (<b>a</b>) and 1979 (<b>b</b>) image sets with a spatial resolution of 10 m after the removal of any spurious elevation values. The upper end of the color bar is set to 550 m to highlight the glacier’s surface features. The gaps in the data are blunders removed from the point clouds post-stereo-processing.</p> Full article ">Figure 7
<p>1978 (<b>a</b>) and 1979 (<b>b</b>) are Brecher’s [<a href="#B14-remotesensing-13-00021" class="html-bibr">14</a>] elevation data converted from the International 1924 ellipsoid to WSG84 XZY values. 1978 (<b>a</b>) and 1979 (<b>b</b>) DEMs interpolated from the WGS84 XYZ values converted from the International 1924 ellipsoid. (<b>c</b>,<b>d</b>) are the 1978 and 1979 interpolated grid results from differencing the originally processed elevations from the SfM elevations.Note that while there are two separate color bars, the scale bar is the same for all four maps.</p> Full article ">Figure 8
<p>Scatter plots of the original analog elevation processing values with the SfM processing elevations (DEM of difference (DoD)) for 1978 (<b>a</b>) and 1979 (<b>b</b>).</p> Full article ">Figure 9
<p>Stable terrain elevation scatter plots for 1978 vs. 1979 DEMs (<b>a</b>) 1978 vs. present-day DEMs (<b>b</b>), and 1979 vs. present-day DEMs. (<b>c</b>).</p> Full article ">Figure 10
<p>(<b>a</b>) Velocities from elevation slopes. The missing section in the middle of the grid is due to poor correlations that left a gap too large to interpolate accurate magnitudes. (<b>b</b>) Brecher’s [<a href="#B14-remotesensing-13-00021" class="html-bibr">14</a>] gridded velocities from contours. (<b>c</b>) Difference map of the two velocities. The line and labeled points represent the profile plot in (<b>d</b>). The points represent points along the profile in kilometers. (<b>d</b>) Velocity profiles of both velocities with the grounding zone highlighted in the dashed vertical lines.</p> Full article ">Figure 11
<p>(<b>a</b>) Frequency histogram of all of the velocity differences. (<b>b</b>) Frequency histogram of just those differences that fall within ±2 <math display="inline"><semantics> <mi>σ</mi> </semantics></math> of the mean. The widths of the bars do change when the new frequencies are calculated.</p> Full article ">Figure 12
<p>The hydrostatic equilibrium boundaries, calculated from historical and present-day elevation sets.</p> Full article ">Figure 13
<p>Surface depression geometry: The boxes in (<b>a</b>) show the locations of the depression in 1979 and in 2017 with a 2019 Landsat 8 OLI image in the background. The grey line passing through the yellow box is the CReSIS flight path for the echogram in (<b>b</b>). (<b>b</b>) A CReSIS echogram collected in 2011. The red box highlights the basal crevasse replaced[id=SFC](responsible for generating the surface depression) which is enlarged and also outlined in red. responsible for generating the surface depression. (<b>c</b>) 1979 (blue box in (<b>a</b>)) and 2017 (yellow box in (<b>a</b>)) DEMs and profile lines over the surface depression. While the profile lines are the same length, they follow slightly different flow paths which is due to the ice spreading as it leaves the fjord and enters the ice shelf. (<b>d</b>) Plots of the elevations from the profiles in (<b>c</b>).</p> Full article ">
17 pages, 8857 KiB  
Article
A Satellite-Based Climatology of Wind-Induced Surface Temperature Anomalies for the Antarctic
by Günther Heinemann, Lukas Glaw and Sascha Willmes
Remote Sens. 2019, 11(13), 1539; https://doi.org/10.3390/rs11131539 - 28 Jun 2019
Cited by 8 | Viewed by 4043
Abstract
It is well-known that katabatic winds can be detected as warm signatures in the surface temperature over the slopes of the Antarctic ice sheets. For appropriate synoptic forcing and/or topographic channeling, katabatic surges occur, which result in warm signatures also over adjacent ice [...] Read more.
It is well-known that katabatic winds can be detected as warm signatures in the surface temperature over the slopes of the Antarctic ice sheets. For appropriate synoptic forcing and/or topographic channeling, katabatic surges occur, which result in warm signatures also over adjacent ice shelves. Moderate Resolution Imaging Spectroradiometer (MODIS) ice surface temperature (IST) data are used to detect warm signatures over the Antarctic for the winter periods 2002–2017. In addition, high-resolution (5 km) regional climate model data is used for the years of 2002 to 2016. We present a case study and a climatology of wind-induced IST anomalies for the Ross Ice Shelf and the eastern Weddell Sea. The IST anomaly distributions show maxima around 10–15K for the slopes, but values of more than 25K are also found. Katabatic surges represent a strong climatological signal with a mean warm anomaly of more than 5K on more than 120 days per winter for the Byrd Glacier and the Nimrod Glacier on the Ross Ice Shelf. The mean anomaly for the Brunt Ice Shelf is weaker, and exceeds 5K on about 70 days per winter. Model simulations of the IST are compared to the MODIS IST, and show a very good agreement. The model data show that the near-surface stability is a better measure for the response to the wind than the IST itself. Full article
(This article belongs to the Section Atmospheric Remote Sensing)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Map of the Antarctic with topography (isolines). Permanent research stations are marked by red squares. Ice shelf areas are light blue (FRIS = Filchner-Ronne Ice Shelf, RIS = Ross Ice Shelf). The blue rectangles mark the focus areas of this study. Data source: RAMP2 ([<a href="#B9-remotesensing-11-01539" class="html-bibr">9</a>]). Part (<b>b</b>): As (<b>a</b>), but for the study area in the eastern Weddell Sea with SWG = Stancomb-Wills Glacier, LI = Lyddan Island, GG = Goldsmith Glacier, SG = Slessor Glacier. Part (<b>c</b>): As (<b>a</b>), but for the study area of the Ross Ice Shelf with BG = Byrd Glacier, NG = Nimrod Glacier.</p> Full article ">Figure 2
<p>Schematics of the vertical temperature structure in the katabatic wind (black line) and a weak-wind ice surface (blue line).</p> Full article ">Figure 3
<p>Example of katabatic warm signatures (Moderate Resolution Imaging Spectroradiometer (MODIS) IR image 2 August 2015, warm = dark, data source: NASA Worldview) and topography from Cryosat-2 data [<a href="#B19-remotesensing-11-01539" class="html-bibr">19</a>]).</p> Full article ">Figure 4
<p>Mean daily coverage 2002–2017 of cloud-free pixels (topography as isolines every 500 m).</p> Full article ">Figure 5
<p>Mean cloud-free surface temperature for winter (April–September) 2002 to 2017 (isolines = topography every 500 m, temperatures outside the range in grey).</p> Full article ">Figure 6
<p>Mean surface temperature anomaly for the RIS for winter (April–September) 2002 to 2017 (isolines = topography every 500 m). The reference area is marked by the box over the ice shelf, the exit areas for both the Byrd and Nimrod glaciers (see <a href="#remotesensing-11-01539-f001" class="html-fig">Figure 1</a>c) are marked by crosses.</p> Full article ">Figure 7
<p>Surface temperature anomaly distribution (1K bins) for winter (April–September) 2002 to 2017 for the exit regions of a) Byrd Glacier and b) Nimrod Glacier (marked by crosses in <a href="#remotesensing-11-01539-f006" class="html-fig">Figure 6</a>). The red line marks a value of +5°C.</p> Full article ">Figure 8
<p>Box-whisker plot for the surface temperature anomaly for different months for winter (April–September) 2002 to 2017 for Byrd Glacier (<b>a</b>) and Nimrod Glacier (<b>b</b>). The median, the 25 and 75% percentiles are plotted as the box, the 10 and 90% percentiles are plotted as error bars.</p> Full article ">Figure 9
<p>As <a href="#remotesensing-11-01539-f006" class="html-fig">Figure 6</a>, but for the eastern Weddell Sea. The green box marks the slope area, the blue box marks the surge area, the black box marks the reference area.</p> Full article ">Figure 10
<p>As <a href="#remotesensing-11-01539-f007" class="html-fig">Figure 7</a>, but for the eastern Weddell Sea for (<b>a</b>) the slope area and (<b>b</b>) the surge area.</p> Full article ">Figure 11
<p>Box-whisker plot for the surface temperature anomaly for different months for winter (April–September) 2002 to 2017 for the eastern Weddell Sea for the slope (<b>a</b>) and surge areas (<b>b</b>). The median, the 25 and 75% percentiles are plotted as the box, the 10 and 90% percentiles are plotted as error bars.</p> Full article ">Figure 12
<p>Daily composite of MODIS surface temperature (left column) and simulated CCLM daily averages of surface temperature, MSLP (isolines) and 10m-wind vectors (right column) for 30 April 2014 (upper row), 1 May 2014 (middle row) and 2 May 2014 (lower row).</p> Full article ">Figure 13
<p>Time series of daily averages of MODIS ice surface temperature (IST) (blue) and CCLM 10 m-wind speed (red) for the slope (<b>a</b>) and surge areas (<b>b</b>) for April and May 2014.</p> Full article ">Figure 14
<p>IST from MODIS and CCLM for the surge area for April and May 2014 (<b>a</b>) and for winters 2002–2016 (<b>b</b>). The blue line indicates the linear fit.</p> Full article ">Figure 15
<p>IST difference between surge area and reference area and corresponding CCLM 10 m-wind speed difference for (<b>a</b>) April and May 2014 for all days (red symbols) and days with the downslope wind (black symbols) and (<b>b</b>) winters 2002–2016 for the days with the downslope wind. The blue line indicates the linear fit.</p> Full article ">Figure 16
<p>CCLM (T2m-IST) difference as a function of wind speed as for the daily means for 2 May 2014 (<b>a</b>) for the ice shelf areas of BIS and Riiser-Larsen (RLIS) and (<b>b</b>) for the slope area for the height range 50–500 m (temperatures height-corrected with an adiabatic lapse rate). The blue line indicates the linear fit for (T2m-IST) &gt; 3K.</p> Full article ">
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