France - OSR

Specific Project Objectives & Deliverables

Results

Within the frame of the MAISEO project: irrigated crops were mapped over the OSR area and water requirements were estimated with the SAFY-WB model at a regional scale. The model was calibrated and validated against ETR flux measurements performed at the Lamasquère experimental site (see Figure 7).



Figure 7: Evapotranspiration, Water needs, GAI (Green area index) and yield of maize (2006, Lamasquère) observed and modeled with SAFYE model (From M. Battude PhD Thesis, at CESBIO in 2017).
 


Within the frame of the frame of the CICC project: we used a large number of temporal Sentinel-1 together with Sentinel-2-like data to assess the potential of the Sentinel satellites for winter and summer crops monitoring. We applied an adapted multi-image filter to the Sentinel-1 images, taking advantage of the Sentinel-1 dense temporal series to reduce the speckle effect, while preserving the fine structure present in the image, like the crop fields boundaries. The time series of optical NDVI and radar backscatter (VH, VV and VH/VV) were analyzed and physically interpreted with the support of rainfall and temperature data, as well as the destructive in situ measurements (green area index (GAI) and fresh biomass, when available). We showed that dense time series allow to capture short phenological stages and thus to precisely describe various crop development. A better understanding of SAR backscatter and NDVI temporal behaviors under contrasting agricultural practices and environmental conditions will help many upcoming studies related to crop monitoring based on Sentinel-1 and -2, such as dynamic crop mapping and biophysical parameters estimation. Regarding crop mapping, we found that wheat and rapeseed could be better distinguished using VH and VV backscatters between March and July and using NDVI between November and December. Regarding summer crops, we recommend using VH/VV and VV to separate maize, soybean and sunflower during the heading/flowering phase. Results also showed that for barley and maize, both NDVI and VH/VV profiles are in good agreement with the destructive GAI and fresh biomass measurements. Thus, VH/VV ratio could be successfully used for biophysical parameters retrieval and direct biomass assimilation in crop models. VH/VV is also able to detect post-harvest spontaneous regrowth. This is a promising result for applications such as the monitoring of regrowth and intermediate crops for estimating soil carbon storage in the perspective of climate change mitigation.


Figure 8: Observations over winter wheat and rapeseed fields: temporal behavior of optical NDVI, radar VH/VV, VH, and VV, rainfalls and temperatures over winter crops, i.e. 64 wheat crops (in blue) and 10 rapeseed crops (in red). Mean values are represented by dots and standard deviations are represented by the filled color domains surrounding the curves. In the last plot (bottom), temperatures in red were measured at the Sentinel-1 acquisition time 6 a.m. The horizontal red line is the 0°C line. Vertical precipitation bars in blue are drawn in green the same days than Sentinel-1 acquisitions and in red the two days before Sentinel-1 acquisitions, assuming that wet soil due to rainfalls may still affect Sentinel-1 backscatter two days later. Vertical grey bars represent Sentinel-1 acquisition events.

 


Figure 9: Observations on maize, soybean and sunflower fields: temporal behavior of optical NDVI, radar VH/VV, VH, and VV, rainfalls and temperatures over summer crops, i.e. 57 maize crops (in blue), 8 soybean crops (in green) and 116 sunflower crops (in red). Mean values are represented by dots and standard deviations are represented by the filled color domains surrounding the curves. In the last plot (Bottom), temperatures in red were measured at the Sentinel-1 acquisition time 6 a.m. The horizontal red line is the 0°C line. Vertical precipitation bars in blue are drawn in green the same days than Sentinel-1 acquisitions and in red the two days before Sentinel-1 acquisitions, assuming that wet soil due to rainfalls may still affect Sentinel-1 backscatter two days later. Vertical grey bars represent Sentinel-1 acquisition events.

©2015 Joint Experiment for Crop Assessment and Monitoring
© HER MAJESTY THE QUEEN IN RIGHT OF CANADA SA MAJESTE LA REINE DU CHEF DU CANADA (2015)