2 What is new in Collection 5

A number of improvements have been applied to the previous Collection 4 (C4) MODIS VI products. Updates are listed under the following main categories:

Science changes
Structural changes
Processing rules
Metadata changes
New VI products

The most important improvements to the VI products are the new quality-based filtering scheme and a modified compositing method to deal with residual and mislabeled clouds. These changes have positively impacted all the VI products, with improved identification of the least cloudy observation from the daily inputs.

In order to benefit from the presence of two identical data streams (Terra and Aqua) we modified certain production rules. Terra and Aqua data streams are processed 8 days out of phase to provide a quasi-8-day temporal frequency, thus improving the change detection capabilities of the products.

Two new output parameters were also added to the MODIS VI products, the Composite day of the year and Pixel reliability.

Additionally, two new VI products were introduced as the VI Climate Modeling Grid (CMG) series: MOD13C1 and MOD13C2. These are generated at 0.05deg spatial resolution, aggregated as 16-day and monthly composites, respectively. The VI CMG series is a seamless global 3600x7200 pixel data product.

Major changes are outlined as follows:

Improved processing of aerosol- and cloud-contaminated pixels.
Implemented internal data-compression to reduce file size.
Fusion and restructuring of NDVI QA and EVI QA into a single VI QA layer.
Added Composite day of the year and Pixel reliability output parameters.
Improvement of the Constrained View angle - Maximum Value Composite (CV-MVC) compositing method.
- The Maximum Value Composite (MVC) is used when all input days are cloudy.
- The CV-MVC approach was modified to favor smaller composite view angles.
Update of the EVI backup algorithm from SAVI to a 2–band EVI.
Adopted a threshold technique to identify anomalous surface reflectances. over inland water bodies in order to suspend the VI computation. This technique was later dropped from the algorithm. The information is left in this document to alert the user community of this special issue.
Adopted an out-of-phase production approach for Terra and Aqua data streams: both products are kept as two independent 16-day composites, with starting dates separated by 8 day. This scheme increases the temporal frequency of the overall Terra-Aqua VI product.

Full details of introduced changes are described in the document “MOD13 VI C5 Changes Document” (http://landweb.nascom.nasa.gov/QA_WWW/forPage/MOD13_VI_C5_Changes_Document_06_28_06.pdf)