PAT TERN-BASED ASSESSMENT OF 2001/2006 L AND COVER CHANGE OVER THE ENTIRE U.S.Pawel Netzel and Tomasz F. Stepinski

Introduction

Change map

Methods

pawel@netzel.pl stepintz@uc.edu

Poster presented at the IGARSS 2014, July 13-18, 2014, Quebec, Canada

1,2 1 Space Informatics Lab (http://sil.uc.edu/) University of Cincinnati, USA

Dept. of Climatology and Atm. Protection, University of Wroclaw, Poland

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e1 2 3 4 scene a3 at 2006

scene a3 at 2001

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1141 clumps

land cover classes

land cover classes

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<1.0 <0.99 <0.9 <0.8 <0.7 <0.6 <0.5 <0.4

similarity

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change 2006 2001

change 2006 2001

developedhigh intensity

developedmed. intensity

developedlow intensity

developedopen space

cultivatedcrops woodywetlands

open water

deciduousforest

pasture/hay

evergreenforest

ice/snow

barren land

mixedforest

shrub/scrub

grassland

emergentwetlands

We present a post-classification change detection method geared toward assessing land cover

change on continental scale . Instead of tracking transitions of land cover classes on pixel-by-pixel basis the method measures the change in local patterns defined on 4.5 x 4.5 km square scenes (see illustration bellow). A pattern in a scene is represented by a 2D histogram of land cover classes and clump sizes and the level of change is measured as the dis-

similarity between motifs of scene patterns at two time points the Jensen-Shannon similarity measure. The methodology is applied to the National Land Cover Dataset (NLCD) to obtain a 2001-2006 change map of the conterminous U.S.

Fig.1 shows co-registered scenes at

two time points; land cover change is visible. Fig.2 shows (in random colors) clumps - contiguous groups of same-category pixels. Each pixel is assigned two variables - land cover category (one of 16 possible) and clump size category inherited from a clump to which it belongs (one of 14 possible). Clump size categories are categorized clump sizes. Fig.3 shows histograms of scenes pixels with re-spect to the two variables.

Dissimilarity between two histograms A and B is calculated using the Jensen-Shannon divergence (JSD), where H is en-tropy.

Fig.1 Fig.2 Fig.3

JSD(A,B) = H A+B2( ( 1

2 [H(A)+H(B)]-

Map of 2001-2006 pattern-based land cover change over the conterminous U.S. The map is 1045 x 1612 grid with each pixel represent-ing a value of JS similarity (1-JSD) between the same local scene in 2006 and 2001. The smaller the similarity the bigger the change. Most of the U.S. experienced little land cover pattern change between 2001 and 2006 (blue color), however, there are regional exceptions including the southeastern and Gulf regions, the Pacific Northwest region, and the state of Maine. There are also multiple local regions showing change in pattern. Five examples are indicated by letters A to E.

change 2006 2001A

The location of the 2002 Hyman forest fire in Colorado [15]. NLCD shows that this area has been covered by a well-consolidated forest in 2001, but the 2006 map shows a scar left by the fire. Pattern change map shows this location as a red spot.

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change 2006 2001D

The location denoted by the letter Bcoincides with the Great Salt Lake in Utah. The change is due to the lake retreated from its 2001 levels to expose more “barren land” in 2006.

Locations denoted by the letter C corre-sponds to urban growth in the cities of Las Vegas, NV and Phoenix. Pattern change map clearly shows expansion of Las Vegas.

ELinear features on the change map correspond to rivers and their surroundings. In particular, letter E denotes the Rio Grande river in New Mexico. The portion of the Rio Grande river and the associated change in land cover be-tween 2001 and 2006 are shown. The changes can be ex-plained by fluctuating water levels.

Locations denoted by the letter D show from left to right) cities of Kansas City, St. Louis, Indianapolis, and Co-lumbus. These cities experi-enced some moderate level of urban development in their suburbia. Indianapolis is shown.

NLCDclasses

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2001

0.4 0.64 0.58 0.63 0.71 0.71 0.74 0.85 0.84 0.88 0.92 0.93 0.36 0.63 0.67 0.62 0.87 0.79 0.74 0.89 0.88 0.86 0.93 0.96

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11 12 21 22 23 24 31 41 42 43 52 71 81 82 90 950.0

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11 12 21 22 23 24 31 41 42 43 52 71 81 82 90 950.0

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Comparison of different measures of change between scenesIn addition to JSS other methods of scene change are: JSS1 which uses only histograms of land cover classes and capture only changes in class composi-tion of the scene, and the fraction of unchanged pixels (r) which measures percentage of pixels in the scene that did not change land cover label. All measures have values between 0 and 1 but yield different values for the same pair of scenes. Figure to the right shows comparison of the values of these three measures in urban environment (Fig.A) and rural environment (Fig.B)

JSS JSS1 r JSS JSS1 r JSS JSS1 r JSS JSS1 r

Fig. A shows a scatter plot of r vs. JSS1 values for all scenes in the change map. The upper-right corner of the plot groups scenes that show very little change, whereas the lower-left corner of the plot groups tiles that show massive change. The tiles are cen-tered around the diagonal of the plot indicating that, on average, both measures have about the same sensitivity. However, there are outliers; P1 indicates one such outlier.Fig. B shows a scatter plot of JSS1 vs. JSS values for all scenes in the change map. The values of JSS are always smaller or equal to the values of JSS1 indicating that patterns are more susceptible to change than bulk compositions. P2 indicates one scene with high value of JSS1 but low value of JSS.

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Similarity between bulk composition (JSS1)Fraction of unchanged pixels (r)

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Fig.A focuses on outlier P1 - the scene where JSS indicates very little change but about 50% of pixels changed labels. The change in this tile is due to the cyclic nature of forest harvesting and regeneration resulting in a chess board-like pattern of forest, shrub, and grassland; individual pixels change but the bulk composition remains approximately the same. Fig.B focuses on outlier P2 - the scene where JSS1 indicate only moderate change but JSS indicates large change. The changes in this tile are due to deforestation; bulk class composition changes but not very much but pat-tern changes a lot from forest with shrub patches in 2001 to shrub with forest patches in 2006.