NDVI Time Geosmart Asia Locate 18 9 11 April 2018 Multi-temporal remote sensing for spatial estimation of Plant Available Water holding Capacity (PAWC) Sofanit Araya Bertram Ostendorf Gregory Lyle Megan Lewis Spatial Information Group (SIG) School of Biological Sciences
Background Plant Available Water Capacity (PAWC)- Bucket size of a soil Total amount of water available for crops that the soil can store Upper storage limit (saturation) - Lower limit (wilting Point). Source: http://www.regional.org.au/
Background Plant Available Water Capacity (PAWC)- Spatially highly variable => high growth and yield variability In Mediterranean environment differences in PAWC explained a large portion of crop yield variability (Hall et al., 2009)
Background Plant Available Water Capacity (PAWC)- Temporally - strong interaction with climate => yield and growth pattern variability from year to year- flip flop scenario High Low Interaction with rainfall amount and seasonality PAWC modulates the vegetation response to climatic variability (Boydell et al., 2001)
Existing PAWC data in SA The two most used available PAWC data in South Australia: Landscape-scale PAWC map 32 0'0"S Soil landscape map of South Australia 1:100,000 (Hall et al., 2009) 34 0'0"S Legend 36 0'0"S >100 mm 70-100 mm 40-70 mm 20-40 mm <20 mm 38 0'0"S 0 50 100 200 Kilometers 135 0'0"E 140 0'0"E APSoil PAWC measurment locations ± 32 0'0"S 34 0'0"S 36 0'0"S Legend APSOIL_SA 38 0'0"S 0 135 0'0"E 50 100 200 Kilometers 140 0'0"E APSoil database - Point based database of soil PAWC measurement (http://www.asris.csiro.au)
Plant Available Water Capacity (PAWC) Measurement Time consuming Relatively expensive Difficult to choice representative soil sampling locations Source: http://aciar.gov.au/ So alternative approach is needed to be used as a surrogate Source: http://www.soilquality.org.au/
Plant Available Water Capacity (PAWC) Indicators Spatial growth variability or Patchiness Temporal variability So we need to observe Vegetation variability Regular temporal change intra annual time scale Source: http://archive.agric.wa.gov.au
tim e Potential of Remote Sensing Quantify vegetation vigour - Vegetation indices (eg. NDVI) Regular revisiting time Multi- temporal observation => Vegetation growth dynamics Space
NDVI Crop phenology from NDVI Time Crop growth dynamics - inform about the environment including water availability, Observations across different climatic conditions (many years) can provide a novel insight about the spatial variability of the underlying soil
time Materials and Methods MODIS NDVI - Phenological metrics Temporal - 16 days Spatial - 250m 2001 2015 (345 images) Measured Soil PAWC from APSoil (http://www.asris.csiro.au) 256 observation points across SA Rainfall data (http://www.bom.gov.au/) High Spatial resolution of 5km Rainfall data Low
NDVI Phenologic metrics Max Value Onset of Greenness Offset of Greenness 0.8 0.7 0.6 0.5 0.4 0.3 0.2 TINDVI Onset Time Time Max Time A new software package CropPhenology package in R software environment (https://github.com/sofanitaraya/cropphenology/wiki/cropphenology-package) Offset Time 15 Metrics are defined
Spatial Modelling To assess the relationship between Phenological metrics and PAWC across different climatic conditions - A linear mixed effects model PAWC (Phenologic Metrics, Growing season rainfall, Year, sub region, error ) Where : Max Value and Max Time are phenological metrics, GSRF- growing season rainfall Year the observation year and S a dummy variable representing the subregion of the state Ԑ - an error term
Spatial Modelling Maximum NDVI and Time of Maximum NDVI - Positive correlation with PAWC The higher the PAWC the higher the maximum NDVI High PAWC => more water => high greenness (NDVI) The higher the PAWC the later the maximum NDVI attained Crop growth under water stress => faster growth rate
Spatial Modelling Interactions with growing season rainfall indicate stronger relationship at higher rainfall seasons Coincides with previous observation that PAWC Crop growth association is stronger in wet years than dry years.
Spatial Estimation
34 0'0"S Spatial Estimation 0 50 100 200 Kilometers 34 0'0"S 135 0'0"E Predicted PAWC map 140 0'0"E 0"S 36 0'0"S Legend High : 165.851 Landscape-scale PAWC map Low : 10.0094 36 0'0"S 0'0"S ± 0"S 38 0'0"S 32 0'0"S 0 50 100 200 Kilometers Landscape-scale PAWC map 32 0'0"S 32 0'0"S 32 0'0"S 0'0"S 0"S 34 0'0"S 34 0'0"S 34 0'0"S 34 0'0"S 0'0"S Legend High : 165.851 Low : 10.0094 36 0'0"S 0"S 36 0'0"S Legend Legend High Class 1 Class 1 Class 2 Class 3 Class 2 Class 4 Class Low 3 Class 4 Class 5 0 50 100 200 Kilometers 36 0'0"S 36 0'0"S 0 50 100 200 Kilometers 38 0'0"S Class 5 135 0'0"E 0 50 100 200 Kilometers 140 0'0"E 0'0"S Landscape-scale PAWC map 0"S 135 0'0"E 140 0'0"E 0'0"S
Spatial Estimation
Corroboration Challenging! Different method used for creation of these datasets Soil-Landscape map - local knowledge and experience using terrain and air photo interpretation APSoil database - measurements were collected using field and laboratory analysis of soil samples In spite of these difficulty 52% of the pixels were classified into similar categories, with 31% more probability than would have happened by chance.
Conclusion There is a consistent soil PAWC signal in the NDVI dynamics, which can be utilized in understanding of variability for agronomic management purpose. The results demonstrate a strong potential of remote sensing derived phenological metrics as indicators for soil PAWC, providing unprecedented spatial detail for digital soil mapping at broad spatial scales. Hence, the presented method can provide an alternative approach for the future broad scale high-resolution soil mapping with the promising advancement of image fusion techniques