Quantifying rates of soil deflation with Structure-from-Motion photogrammetry in west Greenland

Figures & data

Table 1. Locations and details for the ten deflation patches

Patch ID	Latitude	Longitude	Elevation (m)	Area (m^2)	Date of First	Date of Second	Number of Photos (2014, 2016)
ILGRID1	67.11111	−50.25259	366	92.0	01-07-2014	08-07-2016	59, 54
ILSCARP18	67.11276	−50.25615	391	128.3	03-07-2014	08-07-2016	74, 54
LLGRID5	67.08790	−50.29526	280	47.8	24-06-2014	29-06-2016	63, 43
LLGRID6	67.08782	−50.29544	283	84.3	24-06-2014	29-06-2016	78, 48
SLGRID1	67.03974	−50.53759	146	91.2	30-06-2014	02-07-2016	80, 47
SLGRID2	67.03876	−50.53415	130	87.3	30-06-2014	02-07-2016	56, 37
SLSCARP9	67.03641	−50.54607	154	59.2	06-07-2014	02-07-2016	52, 28
SLSCARP10	67.03696	−50.54942	171	36.9	06-07-2014	02-07-2016	55, 34
TNGRID2	67.01474	−50.75369	275	108.9	22-06-2014	02-07-2016	82, 39
TNGRID4	67.01700	−50.75092	333	118.1	08-07-2014	02-07-2016	75, 59

Figure 1. Map showing the locations of the study sites near Kangerlussuaq, Greenland. TN = Town, SL = Sugarloaf, LL = Long Lake, IL = Inland. For coordinates of study sites, see Table 1. Background is a Landsat-7 image from 2000, courtesy USGS

Figure 2. Four terrestrial photographs of soil deflation patch LLGRID5. Note the scarp, visible in all photos. For scale, the ground control mat is roughly 38 × 44 cm. Photos taken June 24, 2014

Figure 3. Establishment of a local coordinate system for deflation patch LLGRID5. Top: Textured model of patch with camera locations superimposed in blue; distances among three control points in white. Bottom: Resulting coordinate system with origin at point A and x axis along segment AB

Table 2. Tie points and registration error between the 2014 and 2016 models for each site

Patch ID	Number of Tie Points	Registration Error (cm)	Registration Error Used (cm)
ILGRID1	8	0.99	1.0
ILSCARP18	6	0.95	1.0
LLGRID5	7	0.96	1.0
LLGRID6	6	0.65	1.0
SLGRID1	5	0.76	1.0
SLGRID2	5	0.46	0.5
SLSCARP9	4	0.28	0.5
SLSCARP10	5	0.59	1.0
TNGRID2	6	1.00	1.0
TNGRID4	6	0.54	1.0

Table 3. Significance thresholds for scarp and center zones for each patch. The significance threshold was calculated in M3C2 using the registration error unique to each patch and the local surface roughness

Patch ID	Significance Threshold (cm)
	Scarp	Center
ILGRID1	2.1	1.9
ILSCARP18	1.9	1.5
LLGRID5	1.8	2.2
LLGRID6	1.9	1.9
SLGRID1	1.9	1.9
SLGRID2	1.0	0.9
SLSCARP9	0.8	0.5
SLSCARP10	2.1	2.0
TNGRID2	1.4	1.9
TNGRID4	1.9	1.9

Table 4. Percentages of points experiencing significant positive and negative change for each zone at all deflation patches. Averages across sites are reported as mean ± standard error

	Scarp		Center
Patch ID	% Points Significant Negative Change	% Points Significant Positive Change	% Points Significant Negative Change	% Points Significant Positive Change
ILGRID1	6.9	9.1	2.5	1.0
ILSCARP18	14.0	2.1	0.4	0.1
LLGRID5	2.4	1.9	0.4	0.7
LLGRID6	19.1	0.2	0.2	0.1
SLGRID1	8.9	2.4	1.4	2.0
SLGRID2	10.9	7.2	0.8	0.2
SLSCARP9	4.6	6.0	0.7	0.1
SLSCARP10	5.7	2.9	3.8	0.1
TNGRID2	2.5	0.2	0.3	0.6
TNGRID4	12.6	11.4	1.7	1.4
Average	8.8 ± 1.7	4.3 ± 1.2	1.2 ± 0.4	0.6 ± 0.2

Figure 4. Results of M3C2 change detection for the scarp and center zones from two deflation patches, ILSCARP18 (A, C, E, G), and LLGRID6 (B, D, F, H). From top to bottom, the rows show (1) the shapes of the scarp and center zones superimposed on the 2014 point clouds (A–B), (2) the spatial distribution of significant change in green (C–D), (3) the magnitude of change between the 2014 and 2016 point clouds (E–F), and (4) histograms of measured change for the scarp (black) and center (gray) zones (G–H)

Table 5. Magnitude of change detected for scarp and center zones for all deflation patches. For each zone, we report the mean negative change, the mean positive change, the mean for all points, and the standard deviation for all points. Asterisks mark mean values that exceed the significance threshold reported in Table 3. Averages across patches are reported as mean ± standard error

	Scarp				Center
Patch ID	Mean Negative Change (cm)	Mean Positive Change (cm)	Mean Change of All Points (cm)	Standard Deviation of All Points (cm)	Mean Negative Change (cm)	Mean Positive Change (cm)	Mean Change of All Points (cm)	Standard Deviation of All Points (cm)
ILGRID1	−1.5	2.0	0.2	2.6	−0.8	0.6	−0.1	1.4
ILSCARP18	−1.8	1.0	−1.0	2.2	−0.4	0.2	−0.2	0.5
LLGRID5	−0.9	1.0	−0.1	1.3	−0.4	0.5	0.1	0.7
LLGRID6	−1.9*	0.5	−1.5	2	−0.4	0.3	−0.2	0.5
SLGRID1	−2.1*	1.7	−1.2	2.9	−0.8	0.8	−0.3	1.2
SLGRID2	−1.4*	1.1*	−0.3	2.2	−0.3	0.3	0	0.4
SLSCARP9	−0.7	0.9*	0.1	1.3	−0.3	0.2	0	0.4
SLSCARP10	−1.2	1.2	−0.4	1.9	−1	0.2	−0.3	1.1
TNGRID2	−0.9	0.5	−0.6	1	−0.4	0.5	0.1	0.7
TNGRID4	−2.5*	2.4*	−0.3	3.7	−0.7	0.7	−0.3	1.2
Average	−1.5 ± 0.2	1.2 ± 0.2	−0.5 ± 0.2	2.1 ± 0.3	−0.6 ± 0.1	0.4 ± 0.1	−0.1 ± 0.05	0.8 ± 0.1

Figure 5. Examples of negative and positive change along two scarps, LLGRID6 (A, C, E) and ILGRID1 (B, D, F). From top to bottom, the rows show (1) the 2014 point clouds, with the locations of the cross-sections in white (A–B); (2) the magnitude of change between the 2014 and 2016 point clouds (C, D); and (3) cross-sections through the 2014 (green) and 2016 (orange) point clouds (E, F)

Figure 6. Examples of vegetation change from ILGRID1 (A, C, E) and LLGRID5 (B, D, F). From top to bottom, the rows show (1) the Betula nana shrubs and outlines (A–B), (2) the spatial distribution of significant change in green (C–D), and (3) the magnitude of change between the 2014 and 2016 point clouds (E, F)

Figure 7. Examples of biological soil crust change from SLSCARP9 (A, C, E) and SLSCARP10 (B, D, F). From top to bottom, the rows show (1) the 2014 point clouds, circles highlight areas of interest (A–B); (2) the 2016 point clouds (C–D); and (3) the magnitude of change between the 2014 and 2016 point clouds (E–F)