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Zimbabwe - Remote sensing based contribution to the assessment of the 2006 Maize harvest prospects
Global Monitoring for Food Security (GMFS)
April 24, 2006

http://www.fao.org/Waicent/Faoinfo/economic/Giews/english/otherpub/gmfs_zwe_2006.pdf

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Introduction
Analysis of available remote sensing data was done in order to estimate the 2006 Maize production
level for Zimbabwe. The analysis was done as part of the GMFS project and was conducted by
Sarmap and VITO.

In general the same approach as described by the FEWSNet report "using remote sensing to assess prospects for the 2006 Zimbabwe maize harvest", issued March 2006 was used, i.e:

• Relating averaged NDVI/VPI to national yield and production
• Estimating production at district level

Different input data and different analysis methods were used and applied.

The first analysis, where NDVI was directly related to production

Data
SPOT-VGT data for the period April 1998 to March 2006 was used. The ten-daily images were
composited to monthly images in order to eliminate as much as possible anomalies due to clouds or
other artefacts. Based on the time series "Vegetation productivity Indicators" were produced and
further analysed. The VPI method was originally developed by C. Sannier based on NOAA AVHRR
data for a study area in Zambia to estimate maize production. The VPI is based on a statistical
distribution of NDVI values put into an historical context. The VPIs were further stratified using the
SADC Regional Land Cover Database.

Dry Matter Productivity images, based on SPOT-VGT NDVI data and ECMWF data, were available
through EC JRC MARS-FOOD (http://www.marsop.info/). Zimbabwe was extracted from the Africawide
images for the period 1998 - 2006.

ASAR AP data (15 m resolution) was acquired over 2 main areas, namely and Mashona provinces.
Quick assessments were done in order to get an overall view of the territory. Although a multitemporal
images were ordered (from September 2005 to June 2006), not all data has been
available. For the Mashona province data was available for 10 October 2005, 29 October 2005 and
13 November 2005. ASAR mosaics were prepared based on the 3 different acquisition dates. For
the area data was received upto February 2006, although there was no consistency in data
received (different dates for different areas). Based on the ASAR AP data a quick visual assessment
was made of cropped areas. This was compared with field pictures, available through FEWSNet
from the 2006 USDA\FEWSnet Crop tour in Zimbabwe (2006) and older landsat TM and ETM+ data.

National Maize production figures for Zimbabwe were obtained from FAO stat for the period 1961 -
2005. Production figures from the Production Estimates and Crop Assessment Division (PECAD) at
USDA have been retrieved for the period 200-2005 from the above mentioned FEWSnet Report.

The SADC Landcover database was available through SADC-RRSU.

ASAR WS data was acquired, however not used given that not all parts of the countries have been
available yet through ESA.

MODIS 250m resolution 16-day composites for the period September 2005 to March 2006 were
obtained through EOS data gateway (http://edcimswww.cr.usgs.gov/pub/imswelcome/).

The administrative boundaries were obtained via FAO and were retrieved from the GAUL database.

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