Enhanced Resolution SSM/I DataJulienne Stroeve, David Long

Introduction

• As part of the ReASON CAN project, we are producing high resolution SSM/I and AMSR-data.

• What this means, is that we now have SSM/I F13 Tb data from 1995-2005. Pixel size of 19-37 GHz channels is 8.9 km (same

as ERS scatterometer images)/ Pixel size of 85 GHz channels is 4.45 km (same as

NSCAT and SeaWinds scatterometer images).

• The data NSIDC currently has is in the polar stereographic projection.

Example of SSM/I High Resolution Images

37H 85V

Options…

• Several projection options are available (standard SCP projections) Polar stereographic EASE-grid Global or just polar?

Grid Projection Options

Options…

• Several projection options are available (standard SCP projections) Polar stereographic EASE-grid Global or just polar?

• Different averaging methods SIR – based on a multivariate form of block multiplicative

algebraic reconstruction. (Early and Long, 2001).o Highest resolution, more artifacts

AVE – first iteration of SIR (weight all measurements for a pixel that have a non-zero spatial response function for the pixel (Long et al., 1993).

o Lower resolution, fewer artifacts

AVE vs SIR

AMSR 6.9H

AVE SIR

Artifacts

• Current SSM/I HIREZ data are produced by averaging all measurements within a single day.

• Artifacts result from the fact that the surface (and/or atmosphere) changed between passes, resulting in inconsistent measurements of the same location.

• So do we want a daily product or two daily images split by local-time-of-day (morning/evening)? Twice daily would allow the diurnal cycle to be examined.

Example of Artifacts

Options…• Several projection options are available (standard SCP projections)

Polar stereographic EASE-grid Global or just polar?

• Different averaging methods SIR – based on a multivariate form of block multiplicative algebraic

reconstruction. (Early and Long, 2001).o Highest resolution, more artifacts

AVE – first iteration of SIR (weight all measurements for a pixel that have a non-zero spatial response function for the pixel (Long et al., 1993).

o Lower resolution, fewer artifacts• Do we want both Tb and time images?

Time is the "effective" time in minutes from the UTC time tag of the data combined to create the pixel.

• Also have the option of Tb standard deviation images. May be useful for ice classification.

• Better spatial coverage and resolution if multiple days are used, but at the expense of reduced temporal resolution.

Using the Enhance Resolution SSM/I

• One application where it may be very useful is in ice motion.

• However, producing high-resolution sea ice concentrations, or melt may not be as straight forward Algorithms that rely on 19/37 differences show

artifacts from the different resolutions of the two channels.

Processing the Data at NSIDC• Currently the processing is done at BYU.• NSIDC could do it, and there is likely a long-term value setting up the enhanced

resolution processing at NSIDC. • Currently BYU does their processing using linux (Red Hat).

Use a big disk array. Requires a machine that is fairly beefy in RAM (at least 2 GB). Computation can be handled by a single processor. To increase the throughput, you must include additional processes by using more

machines, each of which runs one day of data at a time. There is a simple tradeoff between processor speed and time to complete.

Once the raw data are staged, the processing is quite automatic, with the only manual step being doing the Q/A checking and archiving.

• To setup the processing code at NSIDC would require: Compile several custom libraries and programs, modify scripts, and do some testing. Code is written in fortran 77, C, perl, bash and a bit of matlab. One approach: grant BYU remote access to a machine, compile the code, run a sample.

o linux (preferred), solaris, or HPUX machineo NSIDC would modify scripts to automate staging the raw data and arching the results, etc. o Processing for RSS SSM/I and AMSR are very similar so once one it set up, it would fairly easy

to modify the scripts to run the other.

Additional Information

• The entire data set is about 450 GB/yr (for all the different projections. Includes binary files and browse images for SCP

standard regions.

• NSIDC currently has ~375 GB for 10 years (1995-2005) for PS grid, both hemispheres. Both AVE and SIR gzipped Tb binary files in

PS grid with accompanying gif images.• EASE grid is about 52 GB/yr (Greenland =

1.42 GB/yr).