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JECAM | Joint Experiment for Crop Assessment and Monitoring

Senegal - Bambey

Project Overview

Project Objectives


Project Reports

2016 Site Progress Report

2015 Site Progress Report

Publications:

Ndao B. (Cirad/CSE), Thiaw I. (Cirad/CSE), Soti V. (Cirad/ CSE)Apport des images Pléiades pour la caractérisation d’un parc agroforestier dans la zone de Bambey (Région de Diourbel/ Sénégal) - – International congress : XIIIe journées du Réseau Télédétection du 17 au 19 Février 2015, Dakar, Senegal.

Soti V. (Cirad, CSE), Billand C. (Cirad), Thiaw I. (Cirad/CSE), Lelong C. (Cirad), Brevault T. (Cirad), Thiaw C. (ISRA, CNRA) Apport de la très haute résolution spatiale à l’élaboration d’un protocole d’échantillonnage spatial pour l’étude de l’effet du paysage sur la régulation naturelle des ravageurs du mil dans la zone de Dangalma au Sénégal. - International congress : XIIIe journées du Réseau Télédétection du 17 au 19 Février 2015, Dakar (Senegal)

Brévault T., Renou A., Vayssières J.F., Amadji G.L., Assogba Komlan F., Diallo M.D., De Bon H., Diarra K., Hamadoun A., Huat J., Marnotte P., Menozzi P., Prudent P., Rey J.Y., Sall D., Silvie P., Simon S., Sinzogan A., Soti V., Tamo M., Clouvel P. 2014. DIVECOSYS: Bringing together researchers to design ecologically-based pest management for small-scale farming systems in West Africa. Crop protection, 66 : 53-60.

Ndao B : « Systèmes agroforestiers en zone sèche et régulation naturelle des insectes ravageurs des cultures : réalisation d’une carte d’occupation du sol dans la zone arachidière de Bambey au Sénégal » Master2 report- Janvier 2015


Implementation Plans

In situ Data

Vegetation field data collected in Bambey study area and used for satellite image processing was as follows.

Table 1   Vegetation Field Data Collected in Bambey Study Area

For each culture and trees, we collected geographic information with the GPS, the types, the species and the states of the culture or tree (Figure 1). Weekly rainfall data from 2013 to 2015 was collected by the ISRA/CNRA Bambey Institute.

Figure 1 Pléiades Image Showing Different Tree Species in Bambey Study Area

 

 

Plans for Next Growing Season

To build on these first results in the near future, and especially to improve identification of trees, we plan to use satellite images with a richness of bands and a high revisit time, such as the Sentinel-2 sensors which have 13 spectral bands during the dry season when trees are leafy. 


Site Description

Locations

Senegal - Bambey
Site Extent   Centroid: 14.725210, -16.567357
Top left: 14.819407, -16.660269 Bottom Right: 14.625431, -16.468897

Typical Field Size (Area): Around 200m2

Crop Types: Millet, Groundnuts and Maize

Typical Crop Rotation: Millet and Groundnuts

Crop Calendar: July to the end of October

Climate and weather: Sub-Saharan climate with a wet season from September to November and a dry season from December to August.

Soil Texture: Ferruginous tropical sandy soils (Joor and Deck soils)

Landscape Topology: Low slope, 30 m mean elevation

Soil Drainage Class: Very poorly drained, no irrigation

Irrigation Infrastructure: Wells and forages

Agricultural methods used: Low level mechanization dominated by drought animal and manual labour

Figure 1: Land cover map of Bambey study area


Specific Project Objectives & Deliverables

Results

Millet and Groundnuts Identification with Optical and Radar Sensors

Comparing the three maps that we created using Pleiades data alone (2013/01/16; 2013/12/31, 2014/10/30), results show that the millet and groundnuts crops are better classified during the dry season (2013/01/16; 2013/12/31), with respectively 81.4 and 82 % of good ranking. Indeed, contrary to all expectations, in the wet season (2014/10/30), the millet is only classified well in 47% and 30 % for the groundnut with the Pleiades image acquired in October 2014 used alone.
On the other hand, the combination of the Pleiades image with the Landsat-8 time series in 2014 allowed to improve the classification (Random forest classification) with 80% of millet and groundnuts well classified and also to discriminate other crops which was technically impossible during the dry season (Figure 1). Indeed, images acquired during the wet season allowed classifying the Niébé with 68.48%, the sorghum with 97.71%, the fallows with 89.83 % and the pastureland with 79.35% accuracies.

Figure 1 Land Use Map derived from the Combination of one Pleiades Image and Landsat-8 Time Series Acquired during the Wet Season 2014

 

Using the Normalized Difference Vegetation Index (NDVI) of the Landsat-8 image series, we also studied the phenological state of the main cultures (see Figure 2 below). The NDVI allows one to follow the state of the cultures during the wet season. Most of them began to develop their leaves around August 15, and were mature with dense vegetation cover at the beginning of October 2014.

Figure 2 NDVI Temporal Profiles derived from Landsat-8 Time Series of the Main Cultures in the Bambey Area during the Wet Season 2014

 

Millet and Groundnuts Conditions with a Radar Sensor during the Rainy Season 2014

We also tested a time series of TerraSAR-X radar images in Bambey study area for crop discrimination and also to study the dynamics of their phenological states. After image calibration, different polarimetric parameters such as Shannon entropy and Pauli decomposition and methods as unsupervised classification based on H/A/α parameters and the SEaTH algorithm were performed. Unfortunately, these methods were not as effective in discriminating groundnuts from millets or in following their phenological states as the optical sensors tested (Figure 3).

 

Figure 3 Millet and Groundnuts Temporal Profiles Showing the Shannon Entropy Mean derived from TerraSAR-X Time Series in Bambey Area during the Wet Season 2014

 

Evolution of the Crops and Trees since 1968

Our aim in this study is to follow the agricultural spatiotemporal dynamics in the Niakhar area close to Bambey village since 1968. We want to measure the evolution of the crop to the detriment of the natural vegetation and more especially the trees which are very important for soil fertilization, for biodiversity conservation and also for the people’s needs (firewood, medicine, fodder…). To achieve that, we acquired from the CSE Institute archived satellite photography from the Corona American mission in 1968, which had 2 m spatial resolution. We also acquired two Spot 6-7 satellite images within the framework of the JECAM Program. We recently performed the ortho-rectification of the images and now we plan to map trees (species if possible) and the groundnut and millet crops.

Figure 4 Corona Images, 1968


In Situ Observations

  1. Parameter: species, size, density, height, phenoloical activity, geolocation
    Data Collection Protocol:

    Field surveys were conducted during February 2013, 2014 during the dry season when trees are leafy, and in September 2014 corresponding to the crop growing season.

    Frequency:

EO Data Requirements

Approximate Start Date of Acquisition: August (July preferred)
Approximate End Date of Acquisition: End of September (End of October preferred)
Spatial Resolution: 20m in XS and 1m in Pan mode
Temporal Frequency: 1 image per month
Latency of Data Delivery: 1 month
Wavelengths Required: B, G, NIR, R, Red Edge
Across Swath: N/A
Along Track: N/A

SAR Data Requirements

Approximate Start Date of Acquisition: August (July preferred)
Approximate End Date of Acquisition: October (November preferred)
Spatial Resolution: 1m
Temporal Frequency: 1 image per month
Latency of Data Delivery: 1 month
Wavelengths Required: stripNear_007R
Polarization Dual polarization: HH/VV
Incidence Angle Restrictions: Less than 25 degrees
Across Track: N/A
Along Track: N/A

Locations

Senegal - Bambey

Centroid
Latitude: 14.725210
Longitude: -16.567357

Site Extent
Top left
Latitude: 14.819407
Longitude: -16.567357
Bottom Right
Latitude: 14.625431
Longitude: -16.468897


Optical Sensors

Pléiades
Imaging Mode: XS and panchromatic mode
Spatial Resolution: 2 m in XS and .5 m in Pan. mode
Acquisition Frequency: Once per year
Pre-Processing Level: Orthorectified
Application: - Millet, groundnuts and Maize identification - Millet, groundnuts and Maize surface areas estimation

WorldView2
Imaging Mode: XS and panchromatic mode
Spatial Resolution: 1.8m in XS and 0.46 in Panchromatic mode
Acquisition Frequency: Once per year
Pre-Processing Level: Orthorectified
Application: Tree species identification

Sentinel 2
Imaging Mode: XS and panchromatic mode
Spatial Resolution: 1.8m in XS and 0.46 in Panchromatic mode
Acquisition Frequency: Once per year
Pre-Processing Level: Orthorectified
Application: Tree species identification

JECAM | Joint Experiment for Crop Assessment and Monitoring | Group on Earth Observation

©2013 Joint Experiment for Crop Assessment and Monitoring © HER MAJESTY THE QUEEN IN RIGHT OF CANADA SA MAJESTE LA REINE DU CHEF DU CANADA (2012)