Improved OSI SAF Sea Ice Products
The OSI SAF team is now ready to introduce improved versions of the sea ice concentration, edge, type and
low resolution products. In an overlapping period both the new and old products will be available, for
users to test the new products before the new products fully replaces the existing products.
How to access the products in the overlapping period
The new products will be available on this ftp-server:
ftp://osisaf.met.no/prod_test/ice/
The old existing products are as usual available in the directory for the operational products:
ftp://osisaf.met.no/prod/ice/
The products are available relevant sub directories; conc, edge, type and drift_lr.
For the sea ice concentration product, the new product will replace the old as the operational product on
4th November 2015.
For the sea ice edge, type and lr drift, the new products will replace the old as the operational products on
15th September 2015.
Changes in the improved ice concentration product (OSI-401-b)
To ensure continuity, the sea ice concentration algorithm in the new and the old products is the same
(Bristol - Bootstrap combination), and the procedure for regional reduction of atmospheric noise is
the same. However, the new product has several advantages compared to the old. The new product is very
similar to the EUMETSAT OSI SAF sea ice climate record (OSI-409) product, which makes them compatible.
The new developments are a direct result of the dialog with our users. The primary improvements in the new product are:
- Temporally and spatially varying uncertainty estimates on every measured ice concentration pixel are computed.
The total uncertainty squared is given as the squared sum of the representativeness uncertainty and the algorithm
uncertainty. The two components are given in the data-file, together with the total uncertainty.
- A land spill-over correction scheme, which is independent of climatology, is used. This means that, unlike the
old product, ice concentrations are now estimated in the coastal zone. A climatology approach is used in OSI-409 for
land-spill-over correction. A physical-statistical methodology is now used in the new product, in preference to the
climatological one.
- Dynamical tie-points are used to improve the sea ice concentration estimates during summer melt. Dynamical
tie-points are also used to reduce sensitivity to interannual and climatic variability in the ice and water signatures,
and sensor drift. Additionally, the dynamical tie-points enable quicker integration of new microwave radiometer data
and eases the combination of different sensors in the same product, in order to improve coverage.
- The confidence level, based on the standard deviation within each gridcell, is given. This, deprecated, variable
is subject to elimination in future products.
Additionally, a mask has been introduced for the Northern Hemisphere to remove data from regions affected by land
spillover (which causes spurious ice in the measurements). In particular, the mask removes ice concentration
measurements for much of the Baltic Sea and lakes:
Much of the Baltic Sea the North Sea close to the North and East coast of Denmark has been masked, due to
the geography of this region causing significant spillover effects.
Data of lakes have been removed, with the exception of central regions of the great lakes in North America and
Lake Ladoga. The data from these regions should be treated with caution, as the sea ice concentration algorithm
(which was used to compute the concentrations) has not be validated over lakes.
Relevant documentation
More information on these changes can be found in the following documents:
Algorithm Theoretical Basis Document OSI-401-b
Product User Manual OSI-401-b
Validation Report OSI-401-b
Changes in the improved ice edge and type products (OSI-402-b and OSI-403-b)
The two OSI SAF products, sea ice edge and sea ice type, are also being updated. The new updated sea ice edge
product is labelled OSI-402-b which replaces the existing sea ice edge product, OSI-402-a. The same for the new
updated sea ice type product which is labelled OSI-403-b and replaces the existing product, OSI-403-a.
The algorithm is basically the same for deriving the sea ice edge and sea ice type products. The present
new version of the algorithm has the following updates:
- The major update is that the algorithm has become dynamic in order to be more flexible to account for new
sensors and also to better account for seasonal and interannual variability in the ice properties. The algorithm
is dynamic in the way that the daily ice calculations now are based on a training dataset which continuously is
updated to cover data within the preceding two weeks.
- The new OSI SAF sea ice type product delivered for the Southern Hemisphere is by default "ambiguous" for all
the sea ice.
- Similarly, for the Northern Hemisphere in the summer period from mid-May to mid-October, the sea ice type
product classifies all sea ice as "ambiguous".
Relevant documentation
Algorithm Theoretical Basis Document OSI-402-b and OSI-403-b
Product User Manual OSI-402-b and OSI-403-b
Validation Report OSI-402-b and OSI-403-b
Changes in the improved ice drift product (OSI-405-b)
The OSI SAF Low-Resolution sea ice drift product is now being updated. The new version is labelled OSI-405-b
and numbered 1.6. The main changes are:
- Introduce processing of AMSR2 (onboard JAXA's GCOM-W1). It complements the SSMIS-F17 and ASCAT-A products,
and allows for increased accuracy of the multi-sensor ice drift product.
- Final switch of dY sign. Since 2013, the OSI-405 product has been distributed with an interim file format, introducing
a switch of sign for the dY variable, and a status_flag encoded as byte (instead of short). This change is now made
permanent. Please update your software if you are using these two variables (the other variables are unchanged).
Relevant documentation
Algorithm Theoretical Basis Document OSI-405-b
Product User Manual OSI-405-b
Validation Report OSI-405-b
Contact
For questions, please contact us on osisaf-manager[at]met.no.
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