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Mapping irrigated area: Development of an automated approach based on crop phenology through earth observation data
 

Mapping irrigated area: Development of an automated approach based on crop phenology through earth observation data

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Higher resolutions and new data processing capacity are greatly improving our ability to map irrigated areas in Asia and Africa. But areas estimated are higher than national statistics. These ...

Higher resolutions and new data processing capacity are greatly improving our ability to map irrigated areas in Asia and Africa. But areas estimated are higher than national statistics. These differences can be attributed to factors such as inadequate accounting of informal irrigation.

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  • MODIS NDVI data set250m resolutionAvailable for every 16 days from 2000 onwardsGlobal coveragePre-processed standard data product allow comparison between imagesThe only data set available free of cost, consistently, with a global coverage

Mapping irrigated area: Development of an automated approach based on crop phenology through earth observation data Mapping irrigated area: Development of an automated approach based on crop phenology through earth observation data Presentation Transcript

  • Photo:DavidBrazier/IWMI www.iwmi.org Water for a food-secure world Mapping irrigated area: Development of an automated approach based on crop phenology through earth observation data Team: Salman Siddiqui, Sajid Pareeth, Kiran M. C., Rajah Ameer, Darshana Wickeramasinghe, Cai Xueliang, Ajith Jayasekare Side Event: Use of Remote Sensing and GIS Tools in the Irrigation Commands to assist planning and management 1st. World Irrigation Forum 29 September to 5 October, Mardin, Turkey
  • www.iwmi.org Water for a food-secure world Why use RS for Irrigated Area? • Location of irrigated areas • Seasonality of irrigation • Map informal irrigation (GW, small reservoirs, tanks etc.) • Overcome limitations of conventional methods • Provide operational irrigation mapping services An entire state can have one irrigated area % Precise location of irrigation mapped Single crop Continuous crop Double crop y = 0.983x + 0.416 0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70 Province wise Cultivated Area in Pakistan 1990-91 vs 99-2000 Irrigated areas between 1990- 91 vs. 99-2000 for the 4 provinces is almost the same as per the Agricultural Census reports
  • www.iwmi.org Water for a food-secure world Opportunity to update (G)IAM • Data available at higher spatial resolution • Good temporal coverage • Availability of better hardware and software for processing large data sets. • New algorithms in image classification – ‘object based image analysis’ • Impact of climate change and rapid urbanization is more visible during last decade
  • www.iwmi.org Water for a food-secure world Current IWMI Mapping Irrigation Areas Irrigated Area Mapping • South Asia • Asia • Africa
  • www.iwmi.org Water for a food-secure world • MODIS NDVI data set – 250m resolution – Available for every 16 days from 2000 onwards – Global coverage – Pre-processed standard data product – The only data set available free of cost, consistently, with a global coverage • IRS – AWiFS – Spatial Resolution – 56 m – Large swath – 740 km – Spectral resolution suitable for vegetation study Level 1 Level 2 Data and Method : South Asia
  • www.iwmi.org Water for a food-secure world Image classification steps Original Image Segmented Image ISOCLASS Classified Image Recoded Image
  • www.iwmi.org Water for a food-secure world Country Irrigated area (million ha) Rainfed Area (million ha) Total Area (Irrigated + Rainfed) Nepal 4.3 0.5 4.8 Pakistan 21 6.7 27.7 Sri Lanka 0.7 0.4 1.1 India 169 31 200 Bhutan 0.2 0.06 0.26 Bangladesh 11 0 11 Total cropped area 206.2 38.66 244.86 South Asia Irrig. Area Map
  • Comparison : Past and Current Products 2006 GIAM Product Nepal Example 2012 SAIAM Product
  • www.iwmi.org Water for a food-secure world Irrigated Area Mapping Asia Based on MODIS (Terra & Aqua) Product : MOD13Q1 (16Day NDVI Composite) Spatial Resolution : 250m Temporal Range : Jan. 2009 to Dec. 2011 No. Tiles/Images : 4,140
  • www.iwmi.org Water for a food-secure world Identifying Croplands using Satellite Images • Diverse reflectance properties according to the crop and growth stages • Conventional mapping techniques have limited success using coarse resolution images • Need generic methods to separate croplands from natural vegetation • Natural vegetation and croplands exhibit different seasonal characteristics
  • www.iwmi.org Water for a food-secure world Identifying Irrigated Areas • Analyze the intra-annual vegetation changes • Much of Asia has one significant rainfall season • Natural vegetation undergo one annual cycle of growth and drying up • Irrigated, double crop areas likely to have two cycles • Single crop areas would have one annual cycle • Fourier transformation of the annual NDVI curve to identify the cyclic characteristics
  • www.iwmi.org Water for a food-secure world Fourier Analysis • Used to analyze the harmonic nature of time-series data • decompose the complex curve into individual component curves • identify the harmonic nature of the dominant signal • estimate the time of the wave peak
  • www.iwmi.org Water for a food-secure world Fourier Analysis Fourier transformation to analyze the seasonality Dominant annual cycle indicate single crop areas Dominant semi-annual cycle indicate irrigated double crop areas NDVI time series First harmonic Second harmonic Third harmonic
  • Methodology : Asia Manual Method stack Imagestack Imagestack Imagestack ImageNDVI 3year Image Stack ISO-Data Classification (100-1000 class)(100-1000 class)(100-1000 class)(100-1000 class)(100-1000 class) Classified Image (100-1000 classes) Temporal Signature Extraction Signature textSignature textSignature textSignature textSignatures Signature Aggregation K mean Classification Class Assignment Fourier Smoothing Filter Smooth Temporal Signature No of peaks Peak Duration Mean NDVI Peak Starting date(s) Peak date(s) NDVI slope STD NDVI Peak NDVI value(s) Visual Signature Analysis
  • www.iwmi.org Water for a food-secure world Irrigated Area Map Asia
  • www.iwmi.org Water for a food-secure world Irrigated Area Mapping : Africa Based on MODIS (Terra & Aqua) Product : MOD13Q1 (16Day NDVI Composite) Spatial Resolution : 250m Temporal Range : Sept. 2010 to Sept. 2012 No. Tiles/Images : 1,840 Work in Progress!!!!
  • www.iwmi.org Water for a food-secure world Mapping Agriculture in Africa - Challenges • Poor performance of the rapid mapping techniques used for Asia • Cropland – Savanna/ Open forest mosaic • Sparse natural vegetation – low contrast between agriculture and adjacent open landscape • Small farm size – interspersed with natural vegetation • Many farms are < 2 ha – MODIS pixel size is ~6.25 ha
  • www.iwmi.org Water for a food-secure world Approach • Modified the methods adopted for Asia • Developing a rule-based, pixelwise mapping technique to characterize the annual vegetation dynamics • Derived NDVI based parameters to capture various aspects of the magnitude and change of seasonal changes of vegetation • Rules developed for each eco-region.
  • Methodology adopted for Africa Annual MODIS – 16 day NDVI Temporal Fourier Analysis Mean NDVI Amplitude 1 Amplitude 2 Phase 1 Phase 2Trend Standard deviation Training Sites from Google Earth Rule based Classification Land Cover Decision Tree Analysis Global Ecoregions Extract Pixel Values Ecoregion 1 Agriculture Amp 2 > Amp 1 Irrigated + Rainfed FALSE Monthly Rainfall Temporal Fourier Analysis Rainfall Phase 1 Analyse concurr ence RAINFEDIRRIGATED
  • www.iwmi.org Water for a food-secure world Characterizing the seasonality • Measure of green biomass • Harmonic / cyclic characteristics on vegetation change • Measure of intra-annual variability of green biomass • Trend
  • www.iwmi.org Water for a food-secure world • Ecoregion wise classification • Training sites for various land cover types • Classification rules developed through Classification Tree Analysis Rule-based classification
  • www.iwmi.org Water for a food-secure world Mapping irrigated areas - Africa • Identify areas with a significant semi- annual cycle of vegetation change • Use the components resulted from Fourier analysis • Areas with two growing seasons are identified with dominance of the second harmonic term • Demarcate as irrigated areas
  • www.iwmi.org Water for a food-secure world Mapping irrigated areas - Africa • Areas where annual cycle is prominent may consist of both irrigated and rainfed areas. • Compare the correspondence of maximum vegetation growth in a year with the rainfall season. • A mismatch between these two indicate higher chance for presence of irrigation.
  • www.iwmi.org Water for a food-secure world Mapping irrigated areas - Africa
  • www.iwmi.org Water for a food-secure world Critical Issue The areas estimated are higher than the national statistics. These differences have been attributed to factors such as: • Inadequate accounting of informal irrigation (e.g., tanks, minor reservoirs, and ground water) statistics in the National statistics; • Better understanding of the issue of resolution in influencing area; • Misrepresentation of the minimum mapping unit areas; and • Better understanding of definitions of irrigation (e.g., supplemental irrigation).
  • www.iwmi.org Water for a food-secure world Thank you!!!