# Presentation: 034848

## MODIS Vegetation Index Productfrom C4 to C5

**MODIS Vegetation Index Product****from C4 to C5**

**Kamel Didan & Alfredo Huete, ****TBRS Lab.**
**The University of Arizona**

- MODIS Land Collection 5/LTDR Workshop
- University of Maryland University College,  January 17-18, 2007

## Outline

**VI product & Algorithm**
**C5 changes**
**C4 vs. C5**
**Validation statement **
**Future plans (C6?)**

## Algorithm and Product Dependencies

## CV-MVC compositingAVHRR-MVC vs. MODIS-MVC vs. MODIS CV-MVC

## SUMMARY of C5 changes

- Added per pixel reliability (Second most important change)
- Added the composite day of the year to the output
- Replaced the NDVI_QA and EVI_QA with one VI_QA layer
- Restructured the VI_QA data layer to eliminate redundant information

## SUMMARY of C5 changes

- Modified the compositing approach:
- To identify mislabeled cloud
-  Modified CV-MVC to favor smaller view angle
- Adopted a phased production for Terra and Aqua to keep the streams separate while increasing the temporal frequency (Most important change)

## One VI QA layer (restructured) 

**NDVI QA and EVI QA are identical**
**Eliminated this redundancy**

## Composite day of the year

**Useful for temporal comparisons and validation work**

- Southeast US (h10v05)

## Composite day of the year

- Composite period 2000-161

## Per pixel data reliability

- Eliminate the need for QA fields/binary manipulation.
- Ordinal number &  few (4) categories
- Powerful tool for time series/Phenology analysis
- Helps in extracting ‘true’ growing season profile

- Snow/Ice

- Ideal

- Marginal

- Cloud

- Interpolated

- Only for CMG

## Data reliability applications

## Data reliability application

## Global performance

## Phased Production

- Terra & Aqua data are highly identical, but slight differences & other issues makes combining them potentially problematic
- Produced on the same day, so in most cases there is no point in using both (C4 and earlier)
- Improve the use efficiency without combining the two
- Phased production was an ideal solution
- Increased temporal frequency
- Now there is a reason to use both
- Only Aqua will be phased

## Phased Production

**In order for this to work there should be no bias in the selected composite day of the year.**

**nadir aperture **
**door  was closed**

**MODIS-L1B data **
**was not available**

## Phased production

## C4 and C5 Comparisons

## C4 and C5 Comparisons

- Reduced BRDF

- Improved data quality screening

## Cloud reduction

- C4

- C5

## NDVI comparisons

- Consistent & slight
- decrease in C5

## EVI Comparisons

- Consistent & slight
- decrease in C5

## Red LSR Comparisons

## NIR LSR Comparisons

## Noise related Error  budget

## Validation statement

- Maturity= "Validated Stage 2“
- The MODIS Vegetation Index product is retrieved accurately using a state of the art MODIS specific, quality driven, constrained view, maximum value composite method.  For most cloud and snow free, low to no aerosol load, the VI values are very reliable.  Over inland water bodies (rivers, lakes, etc...) surface reflectance inputs and VI values are unstable and should be used with caution. Strong correlations are also found with the nadir-adjusted (NBAR) NDVI and EVI products.  Various field validation campaigns indicate good agreement of VI values for most biomes, and cross sensor correlations (AVHRR, Landsat, SPOT, etc...) are very strong.  The VI product is particularly reliant on coherent inter-band (red and NIR)  atmosphere corrections.  Unstable values may be encountered over more extreme bright or dark surfaces.

## C6 plans (towards CDR)

- MODIS specific
- Completely cloud free & gap filled
- It is pointless to produce/use cloudy observations
- Gaps should be filled with obs. from the historical record (similar to the CMG approach)
- Dynamic composite (First good observation)
- No fixed composite cycle, but VI produced when a good pixel becomes available
- General CDR
- EVI2 for continuity
- EVI Backward compatibility (paper to be submitted) and no-Blue band sensors
- BRDF???