Yale-NUIST Center on Atmospheric Environment Interannual variation of MODIS NDVI in Lake Taihu and its relation to climate in submerged macrophyte region ZhangZhen 2015.07.10 1
Outline Introduction Data acquisition Preprocessing Preliminary analysis Results 2
Introduction It is difficult to track the spatio-temporal variability of vegetation distribution in lakes because of the technological limitations associated with mapping using traditional field surveys as well as the lack of a unified field survey protocol. (zhao et al. 2013) The Moderate-resolution Imaging Spectroradiometer (MODIS) is a payload scientific instrument launched into Earth orbit by NASA in 1999 on board the Terra (EOS AM) Satellite, and in 2002 on board the Aqua (EOS PM) satellite. The instruments capture data in 36 spectral bands ranging in wave length from 0.4 µm to 14.4 µm and at varying spatial resolutions (2 bands at 250 m, 5 bands at 500 m and 29 bands at 1 km). Use NDVI to describe the macrophyte condition in Lake Taihu 3
Data acquisition Data Time Span resolution range NDVI Feb 18 2000-Jun 25 2015 16 day; 250m Taihu Surface Reflectance 217 2013 8 day; 250m Taihu Meteorological data Jan 1 2000-Feb 28 2015 daily DongShan station Radiation data Jun 26 2010-Jun 25 2015 Half-hourly Meilangwan station Normalized Difference Vegetation Index and surface reflectance data is acquired from MODIS Terra product data: MOD13Q1(351 scenes) and MOD09Q1(1 scene) MODIS Data access address: https://lpdaac.usgs.gov/data_access/data_pool Surface reflectance data is used to remove land pixels. Meteorological data is downloaded from China Meteorological Data Sharing Service System. 4
Preprocessing ENVI 4.7 Projection transformation Irregular cutting Band math to wipe off abnormal value Matlab Remove land pixel signal Select NDVI value in a range of zero to one 5
Preliminary analysis Figure 1 Spatial distribution of average NDVI in Lake Taihu from 81 (21 March) in 2000 to 176(25 June) in 2015 6
NDVI 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Year Figure 2 Time series of mean NDVI of the whole Lake Taihu from 2000 to 2015 7
Rainfall (mm) 90 80 70 60 50 40 30 20 10 0 8 40 72 94 136 168 200 232 264 296 328 360 Figure 3 annual variation of multi-yearly average rainfall in Lake Taihu from 2000 to 2015 8
0 10 20 40 KM Figure 4 interannual NDVI spatial distribution of Lake Taihu from 2001 to 2014 9
NDVI 0.3 0.25 0.2 0.15 0.1 0.05 0 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year Figure 5 interannual mean NDVI variation of Lake Taihu from 2001 to 2014 10
NDVI 0.3 0.25 0.2 0.15 0.1 0.05 240 256 240 256 208 224 256 272 256 272 224 240 240 256 224 240 224 240 208 224 224 240 256 272 192 208 272 288 0 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year Figure 6 interannual max NDVI variation of Lake Taihu from 2001 to 2014 July: 182-212 Aug: 213-243 Sep: 244-273 Oct: 274-304 11
Figure 7 Boxplot of multi-year NDVI seasonal variation in Lake Taihu from 2000 to 2015 12
13 Figure 8 Spatial distribution of seasonal average NDVI in Lake Taihu from 2000 to 2015
MLW DPK PTS BFG East Taihu XLS Figure 9 14
Figure 10 Comparison of average NDVI in Region MLW, BFG, DPK, XLS, PTS and East Taihu 15
Figure 11 Time series of meteorological factors(air Temperature, Rainfall, Wind speed, Air Pressure, Relative Humidity) in Dongshan Station 16
1 Jan 17 Jan 2 Feb 18 Feb 6 Mar 22 Mar 7 Apr 23 Apr 9 May 25 May 10 Jun 26 Jun 12 Jul 28 Jul 13 Aug 29 Aug 14 Sep 30 Sep 16 Oct 1 Nov 17 Nov 3 Dec 19 Dec 0 10 20 40 KM Figure 12 Spatial distribution of seasonal average NDVI in Lake Taihu from 2000 to 2015 17
assumption Temperature and Radiation are main factors to control the growth of vegetation. Consider multi-year average meteorological factor value which matching MODIS data s time scale. Exclude the NDVI value in January, February, March and December which is not growing season of aquatic vegetation. 18
BFG East Taihu Figure 13 Relationship of average NDVI and meteorological factor(air temperature and 19 sunshine duration) in Region BFG and East Taihu
Figure 13 Relationship of average NDVI and net Radiation in East Taihu 20
April 20 in BFG May 13 in BFG July 09 in BFG 21
Results NDVI in Lake Taihu has obvious seasonal variation. The minimum happens in winter and the maximum values are clustered between summer and autumn, which mostly occcurs in August and September. The growing season of macrophyte vegetation is from April to November. Interannual trend of NDVI exists difference to some extend. NDVI in macrophyte region (East Taihu and near BFG) has better linear relation with meteorological factor than other regions, which characteristic of vegetation type is close to Landecosystem. 22
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