# Presentation: 900454

## Snow and Sea Ice Algorithm Readiness for C4

- George Riggs
- Dorothy K. Hall
- MODIS Land Collection Version 4 (C4) Reprocessing Review
- 17 December 2002
- GSFC, Greenbelt, MD

## MOD10_L2 --- PGE07

- Benefits of Changes for C4

- Added a new snow cover SDS in which clouds are masked
- with a subset of the cloud test flags (liberal cloud mask)
- from MOD35_L2.
- Enhanced ability to map snow in some situations by decreasing cloud
- obscuration and/or some false cloud detection.   In some situations
- clouds are not masked and falsely identified as snow.
- The enhanced ability to map snow was of greater value
- than the increased erroneous snow mapping.
- This SDS is intended for research and users focused on specific
- regions using only the swath product.
- This new snow cover SDS is NOT passed to L2G and higher products.

## MODIS swath 12 March 2002 1750 UTC 

**MODIS swath 12 March 2002 1750 UTC**

- MODIS bands 1,4,6

- Snow map with conservative cloud mask
- 22% snow; 71% cloud

- Snow map with liberal cloud mask
- 39% snow; 47% cloud

## MODIS Swath 4 June 2001 1805 UTC

**MODIS Swath 4 June 2001 1805 UTC**

- MODIS bands 1,4,6

- Snow conservative cloud mask

- Snow liberal cloud mask
- 3% snow/cloud error

- Lake
- Winnipeg

## MOD10_L2 --- PGE07

- Benefits of Changes for C4

- Raised the estimated surface temperature
- screen threshold to 283K.
- This allowed for enhanced and more accurate
- mapping of snow cover in  transition seasons
- and mixed pixel situations.

## MOD10_L2 --- PGE07

- Remaining Known Issues

- Snow/cloud confusion remains in the,
- 	MOD35_L2 summary result and in the 		subset of cloud tests used for the liberal 		cloud mask.
- Algorithm must be changed for use with Aqua data because of the lost detectors in MODIS band 6.

## MOD10_L2 --- PGE07

- Future Changes in C4 or C5

- Change in use of cloud mask flags in C4.  Affects only the snow SDS generated with liberal cloud mask.  That SDS is NOT passed to downstream products.
- Perhaps revise the estimation of land surface temperature in C4 or C5.
- Integrate a revised snow algorithm for Aqua data in C4. MOD and MYD will probably be different.

## MOD10A1 --- PGE43

- Benefits of Changes for C4

- Changed to Sinusoidal projection, easier for users.
- All MODIS land products changed to sinusoidal projection.

## MOD10A1 --- PGE43

- Remaining Known Issues

- Need for improved scoring algorithm for selecting the observation for a day from the L2G data products. In the current algorithm the most favorable observations are not always selected.
- Current scoring algorithm does not include solar elevation as a criterion.  Selection is biased to chronological order of input data.

## MOD10A1 --- PGE43

- Future Changes in C4 or C5

- Integrate a revised scoring algorithm for selecting the observation for the day from the L2G data.  Revised scoring algorithm will include solar elevation in C4
- 	This change will have a positive effect on 	the MOD10C1 and MOD10C2 products.
- Integrate 500m snow albedo algorithm and SDS in the data product in C4
- Anticipate adding polar projection for the snow products.  (New ESDT for polar projection.)

## MOD10C1 --- PGE46

- Benefits of Changes for C4

- Improved definition of the terminator line resulting in a smoother line.
- Changed snow cover percent calculation to avoid errors in the amount reported
- Integrated a snow impossible mask that eliminates mapping of snow in regions of the world where snow should be a very rare event.

## MOD10C1 --- PGE46

- Remaining Known Issues

- Some snow mapping errors are carried through from the MOD10_L2 and MOD10A1 snow maps.

## MOD10C1 --- PGE46

- Future Changes in C4 or C5

- No major changes are anticipated in C4 or C5

## MOD10A2 --- PGE45

- Benefits of Changes for C4

- Changed to Sinusoidal projection, easier for users.
- All MODIS land products changed to sinusoidal projection.

## MOD10A2 --- PGE45

- Remaining Known Issues

- No major issues are known.

## MOD10A2 --- PGE45

- Future Changes in C4 or C5

- No major changes are anticipated in C4 or C5

## MOD10C2 --- PGE67

- Benefits of Changes for C4

- Improved definition of the terminator line resulting in a smoother line.
- Changed snow cover percent calculation to avoid errors in the amount reported
- Integrated a snow impossible mask that eliminates mapping of snow in regions of the world where snow should never occur.

## MOD10C2 --- PGE67

- Remaining Known Issues

- Some snow mapping errors are carried through from the MOD10_L2 and MOD10A1 snow maps.

## MOD10C2 --- PGE67

- Future Changes in C4 or C5

- No major changes are anticipated in C4 or C5

## MOD29 --- PGE08

- Benefits of Changes for C4

- No significant science changes were made for C4.

## MOD29 --- PGE08

- Remaining Known Issues

- Sea ice and cloud confusion.

## MOD29 --- PGE08

- Future Changes in C4 or C5

- May change coefficients in the split-window technique depending on validation results.  Changes could be made in C4 or C5.
- Changes in technique used to mask clouds.

## MOD29A1 --- PGE44

- Benefits of Changes for C4

- New scoring algorithm for selection of observation of the day and removal of observation coverage restriction greatly increased quality of the data product
- 	Nearly all cells now contain a data
- 	Features are more coherent
- 	Mapping artifacts greatly reduced

## MOD29P1D.A2001198.h0609.003*

- Daily sea ice algorithm C3, Ice Surface Temperature.  Problems observed due to sea ice observation selection algorithm.

- MOD29P1D.A2001198.h0609.004*
- from fourth science test
- Daily sea ice algorithm C4, Ice Surface Temperature.  New scoring algorithm for selection of observations.

## 28 July 2002, north polar projection, tile h07v08 

- MOD29P1 V003
- Sea ice (left), IST (right).
- Observation selected by first layer only
- and restricted to observation coverage
- > 24%.  A great amount of data
- observations are eliminated from the
- map.  Only data from
- one or two swaths, the earliest ones
- of the day are used.  Other later near
- local noon swaths are not used.
- Revised L2G mapping algorithm generated
- the L2G input products.
- Virtually useless sea ice maps
- generated.

- MOD29P1 V004
- Sea ice (left), IST (right)
- Sea ice observation selected by scoring
- algorithm.  Scoring based on solar
- elevation, distance from nadir and
- percent of cover.  No observation
- coverage restriction. Scoring favors
- observations near local noon, close to nadir
- and with most coverage in a cell.
- Revised L2G mapping algorithm generated
- the L2G input products. Very useful sea
- ice maps generated.

**28 July 2002, north polar projection, tile h07v08**

## MOD29A1 --- PGE44

- Remaining Known Issues

- None known.
- Evaluation of version 4 of the product continues.

## MOD29A1 --- PGE44

- Future Changes in C4 or C5

- Significant changes are not expected.

## MOD29C1 --- PGExx

- Benefits of Changes for C4

- New ESDT for the cryospheric research community.
- Daily global, polar view, of sea ice.

## MOD29C1 --- PGExx

- Remaining Known Issues

- Define the product and implement the algorithm code.
- A prototype is done.  Spatial resolution is 4km.  SDS dimensions, 4321x4321. Sea ice by reflectance and ice surface temperature SDSs.  North and South Polar maps in the file.

## MOD29C1 --- PGExx

- Future Changes in C4 or C5

- New ESDT.