ggsps data
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GGSPS Data
How to access data
How to read data
GGSPS or ROLSS ?
• GGSPS– Level 1.5 NANRG and ARG filtered radiances– Level 2 ARG fluxes and unfiltered radiances
from RGP (40 day delay)
• ROLSS– Level 2 ARG, BARG, SHI fluxes and
unfiltered radiances (< 40 days)
Access to GGSPS Datahttp://ggsps.rl.ac.uk/
Registration: Controlled by Imperial.
Access to GGSPS Data“Catalogue”: Catalogue searches only
several search criteria
“Products”: Catalogue searches and retrieval of products
Access to GGSPS Data
Downloading Products
• Three ways to download products:– click on link to an individual file– click on “Download” button
• maximum limit of 600 files
– “Access the most recent data products” (from the “Products” page) … tarred and zipped products in 6 hour bundles.
Structure of Products
• L1.5 NANRG and ARG Products– NANRG (6 individual unrectified images)
• up to 6 radiance datasets (256 x 282)
• up to 6 longitude and 6 latitude datasets
– ARG (2 time averaged rectified images)• 2 radiance, 2 standard dev, 2 valid. flag datasets
• 1 longitude, 1 latitude, 3 viewing angle datasets
• HDF5 Format (Hierarchical Data Format)
HDF5 Files
• Three entities to know about:– Groups: rather like directories, define a
hierarchy within which the data is stored– Datasets: tend to hold one or two dimensional
arrays of data. Has an associated “dataspace”.– Attributes: tend to hold individual values,
sometimes one dimensional arrays, of metadata. Groups and datasets can both have attributes.
NANRG
Groups Datasets Attributes
N A N R G
Q u a ntisa tio n Fa c to r
U n it
L a titu d e (o r E le va tio n)
L o n g itu d e (o r A z im u th )
S h ort W a ve Im ag e 1 S h ort W a ve Im ag e 2
G e o lo ca tion
Num ber of Colum ns in Short W ave Im age 1
...
Q u a ntisa tio n Fa c to r
U n it
S h ort W a ve R ad ia nce Im ag e 1
S h ort W a ve R ad ia nce Im ag e 2
T o ta l R ad ian ce Im ag e 1
R a d io m e try
/
Groups Datasets Attributes
ARGA R G
Q u a ntisa tio n Fa c to r
U n it
L a titude
L o ng itu de
R e la tive a z im u th a n g le
S o la r ze n ith an g le
V ie w in g ze n ith an g le
N x
N y
L ap
...
R e c tif ie d G rid
G e o lo ca tion
Q u a ntisa tio n Fa c to r
U n it
S h o rt W a ve F ilte re d R a d ia n ce
S hort W ave F iltered R ad iance S tand ard D eviatio n
S hort W ave F iltered R adiance V alid ity F la g
T o ta l F ilte red R ad ia n ce
T ota l F iltered R adian ce S tandard D eviatio n
T ota l F iltered R ad iance V alid ity F la g
R a d io m e try
/
Datasets
• Usually signed short integers
• Written out row by row (north-> south); each row west-> east
• use quantisation factor attribute to convert data to correct units:
Converted value = encoded value * quantisation factor
How to read products• HDF5 tools (h5dump, h5ls, H5View)
– useful for seeing what’s in an unknown file
• IDL– IDL v5.6+ (or v5.5 & plug-in) : HDF5– <= v5.5 : HDF4 only. Use h5toh4 to generate
HDF4 GERB products.– bugs in h5_browser/h5_parse
• HDF APIs– write your own Fortran/C/C++/Java/… code
Example (IDL HDF5 interface)
FILE_ID = H5F_OPEN(FileName) ; open file
; open root and radiometry groups
root_group_id = H5G_OPEN(FILE_ID,ROOT_GROUP)radiometry_group_id = H5G_OPEN(root_group_id,RADIOMETRY_GROUP)
; open and read the dataset
SW1_ID = H5D_OPEN(radiometry_group_id,SW_1)SW1Data = H5D_READ(SW1_ID)
; open and read the quantisation factor attribute
ATT_ID = H5A_OPEN_NAME(SW1_ID,QUANTISATION_FACTOR)SW1_QF_Data = H5A_READ(ATT_ID)
H5A_CLOSE, ATT_ID ; close attribute and datasetH5D_CLOSE, SW1_ID
H5G_CLOSE, radiometry_group_id ; close groupsH5G_CLOSE, root_group_id H5F_CLOSE, FILE_ID ; close file
Further Help• Example Code and Simple Tools on GGSPS
Web Site (see “Products” page)
• GGSPS User Guide will appear shortly
• RMIB User Guide available (more info on how to read HDF files)
• NCSA HDF Web Site– http://hdf.ncsa.uiuc.edu/– libraries, tools, tutorial, user guide, reference manual
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