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Product pages » Fractional cover - MODIS, CSIRO Land and Water algorithm, Australia coverage

Fractional cover - MODIS, CSIRO Land and Water algorithm, Australia coverage

Last modified by Matt Paget on 2016/05/03 17:25

Fractional cover - MODIS, CSIRO Land and Water algorithm, Australia coverage

FractCover.V21.2011.177.aust.005.png

Link to the data

DescriptorData linkLayer name
Dataset digital object identifier (DOI)

GeoNetwork recordhttp://data.auscover.org.au/geonetwork?uuid=d478e7a1-9888-4942-a306-3c5015c3585a
ENVI and NetCDFhttps://remote-sensing.nci.org.au/u39/public/html/modis/fractionalcover-clw
Geoserver examplehttp://data.auscover.org.au/geoserverclw:FractCover.V2_2.PV
clw:FractCover.V2_2.NPV
clw:FractCover.V2_2.BS

Data licence and Access rights

ItemDetail
RightsCopyright 2008-2012 CSIRO. Rights owned by the Commonwealth Scientific and Industrial Research Organisation (CSIRO). Rights licensed subject to Creative Commons Attribution (CC BY).
LicenceCreative Commons Attribution 3.0 License, http://creativecommons.org/licenses/by/3.0.
AccessThese data can be freely downloaded and used subject to the CC BY licence. Attribution and citation is required as described at http://data.auscover.org.au/citation. We ask that you send us citations and copies of publications arising from work that use these data.

Alternate title

MODIS NBAR-derived 16-days fractional cover of Photosynthetic Vegetation (PV), Non-Photosynthetic Vegetation (NPV) and Bare Soil (BS).

Abstract or Summary

Data are MODIS NBAR-derived 16-days fractional cover of Photosynthetic Vegetation (PV), Non-Photosynthetic Vegetation (NPV) and Bare Soil (BS). Fractional cover represents the exposed proportion of PV, NPV or BS within each pixel. In forested canopies the photosynthetic or non-photosynthetic portions of trees may obscure those of the grass layer and/or bare soil.

Spatial and Temporal extents

ItemDetail
Spatial resolution (metres)500 m
Spatial coverage (degrees)110.000000 to 155.001329 E, -10.000000 to -45.000512 N
Temporal resolution16 day composite, produced each 8 days
Temporal coverage2000-02-18 to ongoing
Sensor & platformMODIS Terra&Aqua
ItemDetail
Spatial representation typegrid
Spatial reference systemWGS 84

Point of contact

ItemDetail
NameJuan Pablo Guerschman
OrganisationCSIRO Land and Water
Position
EmailJuan.Guerschman@csiro.au
Roleauthor
AddressGPO Box 1666, Canberra ACT 2601, Australia
Telephone+61 2 6246 5880
URL
ItemDetail
NameMichael J. Hill
OrganisationEarth System Science and Policy, University of North Dakota
Position
Emailhillmj@aero.und.edu
Roleauthor
Address
Telephone
URL

Credit

This dataset has been developed by the Environmental Earth Observation Group, CSIRO Land and Water. This work has been partially supported by a NASA Earth Science Enterprise Carbon Cycle Science research program (NRA04-OES-01).

Keywords

ThesauriKeyword
GCMDEARTH SCIENCE > BIOSPHERE > VEGETATION > VEGETATION COVER
CFvegetation_area_fraction
FoREnvironmental Sciences > Ecological Applications = 0501

There are three main thesauri that AusCover recommends:

  1. Global Change Master Directory (http://gcmd.nasa.gov)
  2. Climate and Forecast (CF) convention standard names (http://cfconventions.org/standard-names.html).
  3. Fields of Research codes (http://www.abs.gov.au/ausstats/abs@.nsf/0/6BB427AB9696C225CA2574180004463E?opendocument).

Data quality

The quality of the fractional cover product is dependant on the quality of the MODIS NBAR data, and subject to uncertainties and bias as described in Guerschman et al. (2009). The phased production strategy (i.e. producing a 16-day composite every 8 days) and the combination of the Terra and Aqua sensors in the MCD43A4 collection 5 enhances the chances of obtaining enough cloud-free data for each pixel in each date compared to the same data in collection 4. However, there are still areas with poor data availability, notably in the tropical areas during the monsoonal rains (November to April).

Temporal and spatial completeness is dependent on the completeness of the underlying MODIS NBAR product, MCD43A4. The MODIS NBAR data for the Australian Continent were downloaded from the MODIS Land Products for Australia site (http://data.auscover.org.au/geonetwork?uuid=61226fbe-ec2a-4b86-9e32-4bd96855e400).

Validation status

Field site activities coordination by ABARES (https://remote-sensing.nci.org.au/u39/public/html/modis/fractionalcover-sitedata-abares) will be used to validate the data. Version 2.2 is the first attempt at this.

Related products

ItemProduct link
MODIS Land Products for Australiahttp://data.auscover.org.au/geonetwork?uuid=61226fbe-ec2a-4b86-9e32-4bd96855e400
MODIS Fractional Cover Metricshttps://remote-sensing.nci.org.au/u39/public/html/modis/fractionalcover-metrics-abares
MODIS Fractional Cover Site Datahttps://remote-sensing.nci.org.au/u39/public/html/modis/fractionalcover-sitedata-abares

References

ItemDetail or link
PublicationJuan Pablo Guerschman, Michael J. Hill, Luigi J. Renzullo, Damian J. Barrett, Alan S. Marks, Elizabeth J. Botha (2009). Estimating fractional cover of photosynthetic vegetation, non-photosynthetic vegetation and bare soil in the Australian tropical savanna region upscaling the EO-1 Hyperion and MODIS sensors Remote Sensing of Environment, Volume 113, Issue 5, pp. 928-945. http://dx.doi.org/10.1016/j.rse.2009.01.006
Validation reportGuerschman, JP, Oyarzabal, M, Malthus, TJ, McVicar, TM, Byrne, G, Randall, LA and Stewart, JB (2012), Validation of the MODIS-based vegetation fractional cover product, CSIRO Land and Water Science Report, Canberra, April 2012, available at http://www.clw.csiro.au/publications/science/2012/SAF-MODIS-fractional-cover.pdf

Algorithm summary

Fractional cover was derived using a linear unmixing methodology (Guerschman et al. 2009). This method uses the NDVI and the ratio of MODIS bands 7 and 6 (2100 and 1600 nm respectively). A basic assumption of this method is that areas with high fractions of BS have a flat spectral feature in the shortwave infrared (SWIR) and therefore a relative high (close to 1) ratio of MODIS bands 7 and 6. Areas with high proportion of NPV have a lower reflectance in the 2100 nm region compared to the 1600 nm region and therefore a lower (around 0.6) ratio of MODIS bands 7 to 6. The methodology was originally developed for the Australian tropical savannas and evaluated using field measurements of grass curing in 10 sites of which six are included in the tropical savannas and four are located in grasslands in the west and south east of Australia. We applied the resulting method to the whole Australian Continent.

Product version history

Version labelDetail
Version 1Data produced using the method and the data as described in Guerschman et al. (2009). It uses MOD43A4 collection 4, with a 1km spatial resolution.
Version 2Created using the MCD43A4 collection 5 data, applying the same algorithm as version 1. The main improvements as compared to Version 1 are in the spatial resolution (500m instead of 1000m) and the phased production strategy (16-days composites produced every 8 days).
Version 2.1 (June 2010)

Differs to Version 2 in:

  • Fractional cover values for areas where unmixing was constrained (FLAG=2) were set to 254 (0 in V2.0). This avoids the possibility that the user will use the value of 0 when the fractional cover should be ignored altogether.
  • Algorithm only applied to pixels over Australian Land (ocean and PNG ignored and set to 255).
Version 2.2 (November 2011)

Differs to Version 2.1 in:

  • Location of endmembers was redefined following a validation exercise reported in Guerschman et al. (in press).
  • The main effect of that change was an overall decrease in the fractions of bare soil (BS) and an increase in the fractions of non-photosynthetic vegetation (NPV). The estimates of photosynthetic vegetation (PV) had very low changes.
  • The changes in the endmember locations decreased the RMSE of the three cover fractions from 17% to 14.7% (PV), 25% to 20.6% (NPV) and from 26% to 17% (BS).
  • The reader is referred to Guerschman et al. (in press) for more details on these changes.

Directory, filename and data formats

The subdirectory structure is the following:

./
   v2/
     2000/
     2001/
        .../

Filenames of individual data files have the following format:

       FractCover.YYYY.DDD.aust.005.VV.img

where:

     VV     =  PV is fraction of Photosynthetic Vegetation
               NPV is fraction of non-Photosynthetic Vegetation
               BS is fraction of Bare Soil
               FLAG is a flag that indicates the processing type
     YYYY    = Year (2000 to 2008)
      DDD    = Day of year corresponding to the first day of the 16-day
composite

For example: FractCover.2000.049.aust.005.BS.img corresponds to the fraction of Bare Soil for the 16-day period starting on the day 49 of the year 2000 (i.e. 18 February to 4 March 2000). Each file is stored in BYTE format with values ranging from 0 to 100 (corresponding to the fraction * 100). Pixels with no information in the MODIS NBAR images have a value of 255. An ENVI header is also provided as a file with the same name and suffix "hdr". All data files (.img) have been compressed with the gzip software, and therefore include the extension "gz".

The unmixing method using NDVI and the ratio of MODIS bands 7 and 6 was performed partially constrained. This means that when one of the three fractions is between -Threshold and 0 (or between 1 and 1+Threshold) that fraction is fixed at 0 (or 1) and the other two fractions are recalculated to add 1. The variable Threshold was fixed at 0.2. For a more detailed explanation refer to Guerschman et al (2009). The FLAG image contains, for each pixel, information about the processing type as follows:

0 - Pixel processed normally, unmixing unconstrained.
1 - Unmixing partially constrained (i.e. one of the fractions between -0.2 and 0 or between 1 and 1.2. That fraction capped at 0 (or 1) and the other two fractions recalculated to add 1.
2 - Unmixing constrained and fractional cover not calculated. This happens when one or more of the fractions lower than -0.2 or higher than 1.2. This typically occurs in water bodies and salt lakes. In this case the values of PV, NPV and BS are 254. [Note: in Version 2.0 the values of the three fractions were 0]
255 - MODIS NBAR data not available (typical of clouds during most of the 16 days of the composite). In this case the values of PV, NPV and BS are 255.

A quicklook, with the same name as the data files and suffix png, has been generated. It contains a false color composite of each image with NPV, PV and BS in red, green and blue respectively. In the quicklook images white colours correspond to areas where MODIS NBAR data were not available (FLAG= 255) and ocean. Black areas correspond to areas where FLAG= 2.

Metadata history

DateDetail
2009Metadata creation date
2012-08-31Added Version 2.2 info.
2012-12-10Reformatted to new template.
Added Filename and Product version sections. Added Validation reference.
Tags:
Created by Matt Paget on 2016/05/03 17:25

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