Processing details
Overview
- Coriolis performs the collection of in situ data from various sources
(drifting buoys, oats, ship data,...) received through various networks
with various delivery delays (from real-time - less than 24 hours - to
delayed mode - a few weeks or months later).
- These data are
received and quality-controlled in real-time (and possibly with
additional visual control from an operator) by Coriolis and then
ingested and stored into a relational database. Later delayed-mode
quality controls are applied to the in situ measurements stored in the
database.
- The latest in situ data received and controlled
by Coriolis are delivered to Medspiration system on a daily basis.
- They
are colocated with the satellite datasets collected and archived in
real-time by Medspiration.
- The retrieved satellite match-ups are
then provided back to Coriolis relational database, linked together
with the matching in situ measurements already stored into the
database. Doing so ensures that one gets the latest state of the in
situ values and quality information when extracting the match-up
records from the MDB and thus benefits on the delayed-mode quality
controls performed between the ingestion in and the extraction from the
database by Coriolis on the in situ measurements.
- The match-up
records can be extracted anytime by users either through a web
extraction interface or periodically generated match-up records files.
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Colocation processing
This section presents the basic processing scheme (colocation
algorithm) applied to a given GHRSST-PP dataset to select the match-up
database records.
The first step consists in selecting the relevant in situ data according to the following criteria :
- keeping only the in situ stations matching the satellite datasets
coverage limits (if not global). Only the insitu data located within
these boundaries are considered in the following steps.
- keeping only the in situ stations more recent than 30 days.
Taking into account larger time period would involve scanning to many
data files and would require online storage of large amount of data as
well as too much processing time
For each in situ station, the closest valid satellite pixel to this
station is searched for, with respect to the following search scheme :
- identifying the closest pixel (in spatial distance) to the in
situ station. This pixel may be valid or not, it is the pixel covering
the area in which the in situ station is located.
- extracting the neighbouring pixels in a (approximately) 25km x
25km box centred on the pixel identified above (and therefore on the in
situ data). Each pixel within this box can be considered approximately
at a distance up to 12-13 km from the in situ station. The size in
pixel of the validation box depends on the satellite product
resolution. It is summarized in the table below .
- selecting within this box the closest pixel in time from the in
situ station. Time criteria has therefore precedence on space criteria.
However, if another pixel is closer in space and not older than 5
minutes, it is selected instead : this allows to process correctly the
swath data for which all pixels within the box have more or less the
same time (within a few seconds) : the space criteria should then have
precedence on time. The match-up processing ensures an in situ can only
be colocated once with a given dataset.
- statistics are computed
on the satellite pixels surrounding the in situ measurement(the pixels
contained in the 25km x 25km validation box). They include :
- (a)
the percentage of valid data (= the data for which a sea surface
temperature value is defined and not a default value) within this box.
- (b) the mean sea surface temperature value within this box.
- (c) the standard deviation sea surface temperature value within this box.
- (d)
the respective percentage of pixels within this box having a proximity
confidence value equal to 0,1,2,3,4,5 and 6 (for infrared sensors) or
10,11,12 and 13 (for microwave sensors).
| Product ref |
Satellite |
Sensor |
Resolution |
Box size |
| EUR-L2P-ATS_NR_2P |
ENVISAT |
AATSR |
1 km |
25x25 |
| EUR-L2P-AVHRR16_G |
NOAA-16 |
AVHRR |
9 km |
none |
| EUR-L2P-AVHRR17_G |
NOAA-17 |
AVHRR |
9 km |
none |
| EUR-L2P-AVHRR16_L |
NOAA-16 |
AVHRR |
1-2 km |
none |
| EUR-L2P-AVHRR17_L |
NOAA-17 |
AVHRR |
1-2 km |
none |
| EUR-L2P-NAR16_SST |
NOAA-16 |
AVHRR |
1-2 km |
13x13 |
| EUR-L2P-NAR17_SST |
NOAA-17 |
AVHRR |
1-2 km |
13x13 |
| EUR-L2P-NAR18_SST |
NOAA-18 |
AVHRR |
1-2 km |
13x13 |
| EUR-L2P-SEVIRI_SST |
METEOSAT-7 |
SEVIRI |
10 km |
3x3 |
| EUR-L2P-AMSRE |
AQUA |
AMSRE |
25 km |
3x3 |
| EUR-L2P-TMI |
TRMM |
TMI |
25 km |
3x3 |
| EUR-L4UHFnd-MED-v01 |
Merged |
Merged |
2 km |
13x13 |
| EUR-L4UHFnd-NWE-v01 |
Merged |
Merged |
2 km |
13x13 |
