Mapping the irrigated rice cropping patterns of the Mekong delta, Vietnam, through hyper-temporal SPOT NDVI image analysis

Abstract

Successful identification and mapping of different cropping patterns under cloudy conditions of a specific crop through remote sensing provides important baseline information for planning and monitoring. In Vietnam, this information is either missing or unavailable; several ongoing projects studying options with radar to avoid earth observation problems caused by the prevailing cloudy conditions have to date produced only partial successes. In this research, optical hyper-temporal Satellite Pour l'Observation de la Terre (SPOT) VEGETATION (SPOT VGT) data (1998-2008) were used to describe and map variability in irrigated rice cropping patterns of the Mekong delta. Divergence statistics were used to evaluate signature separabilities of normalized difference vegetation index (NDVI) classes generated from the iterative self-organizing data analysis technique algorithm (ISODATA) classification of 10-day SPOT NDVI image series. Based on this evaluation, a map with 77 classes was selected. Out of these 77 mapped classes, 26 lasses with prior knowledge that they represent rice were selected to design the sampling scheme for fieldwork and for crop calendar characterization. Using the collected information of 112 farmers' fields belonging to the 26 selected classes, the map produced provides highly accurate information on rice cropping patterns (94% overall accuracy, 0.93 Kappa coefficient). We found that the spatial distributions of the triple and the double rice cropping systems are highly related to the flooding regime from the Hau and Tien rivers. Areas that are highly vulnerable to flooding in the upper part and those that are saline in the north-western part of the delta mostly have a double rice cropping system, whilst areas in the central and the south-eastern parts mostly have a triple rice cropping system. In turn, the duration of flooding is highly correlated with the decision by farmers to cultivate shorter or longer duration rice varieties. The overall spatial variability mostly coincides with administrative units, indicating that crop pattern choices and water controlmeasures are locally synchronized. Water supply risks, soil acidity and salinity constraints and the anticipated highly fluctuating rice market prices all strongly influence specific farmers' choices of rice varieties. These choices vary considerably annually, and therefore grown rice varieties are difficult to map. Our study demonstrates the high potential of optical hyper-temporal images, taken on a daily basis, to differentiate and map a high variety of irrigated rice cropping patterns and crop calendars at a high level of accuracy in spite of cloudy conditions

Mapping Rice Seasonality in the Mekong Delta with Multi-Year Envisat ASAR WSM Data

“…We found good agreement in the spatial distribution of single, double and triple rice-cropping schemes compared to previous studies in the Mekong Delta that reported cropping scheme maps with accuracies similar to our product [6,8,49,66,77]. The major driving force behind a farmer's choice of cropping scheme is the availability and management of water [66].…”

“…We suspect that these dynamic changes are also one of the error sources contributing to the low producer accuracy of the single-cropped class compared to the 2005´2010 intersection. Single-cropped, rainfed rice is increasingly diminished in favor of more profitable shrimp and fish farming [8,66,78] and could thusly be misclassified when such a change occurred during our study period. In addition, this cropping scheme is less widely distributed and spatially homogeneous than double or triple crop rice and might therefore be underrepresented in the 2005 land-use map which is based on moderate resolution data.…”

“…Some triple-cropped areas employ a short "Spring´Summer" season between Winter´Spring and Summer´Autumn. Choice of rice variety, cropping scheme and growing season implemented by farmers is highly dependent on the availability of irrigation water and local water management practices leading to a spatially diverse distribution [66]. …”

“…Large parts of the delta are flooded and covered in a new layer of sediments each rainy season; flood-controlled fields experience this every 3 to 4 years without interrupting the rice-cropping scheme [66].…”

An evaluation of flood inundation mapping from MODIS and ALOS satellites for Pakistan

“…Satellite-based flood inundation maps can be a very important input for assessing the progression of floodwaters and the severity of the flood situation. In the past several years, many satellite techniques that use optical sensors have been proposed to detect flood inundation, including National Oceanic and Atmospheric Administration (NOAA)/advanced very high resolution radiometer (AVHRR) (Jain et al 2006), Landsat multispectral scanner system (MSS), thematic mapper (TM) (Hallberg et al 1973;Rango & Solomonson 1974), advanced land imager (ALI) (Amarnath 2013), Indian remote-sensing satellite (IRS) (Jain et al 2006), Satellite Pour l'Observation de la Terre (SPOT) VEGETATION (Nguyen et al 2012) and Terra MODIS (Xiao et al 2005;Sakamoto et al 2007). …”