 |
|
|
|
|
 |
| Announcements |
- TOPEX/Poseidon has now moved well in front of Jason-1 and will no longer violate Jason's 1-km red zone. All remains nominal onboard the spacecraft and we anticipate returning the Poseidon-2 altimeter to an operational state on 13-May, prior to the start of the next Jason science cycle.
- TOPEX/Poseidon (T/P) was decommissioned in orbit in February 2006, and has been adrift ever since. On 07-May, T/P was about 7km (4.3 miles) behind Jason in the same orbit plane and was closing. In terms of time separation, T/P trailed Jason by about 1 second.
TTThe relative along-track phasing between Jason and T/P will soon result in a period of close approaches. Ten events on 08-09 May have been identified where TOPEX will violate a 1-km watch sphere around Jason, with the closest approach of 294 meters occurring on 09-May at 0239z.
TTThe risk of collision between the two spacecraft is exceedingly small, so no collision avoidance maneuver is required. However, there is a significant risk that when T/P drifts below Jason that it could reflect the Poseidon-2 altimeter signal back at Jason at almost full transmit power, seriously damaging the altimeter’s front-end receiver.
TTTo mitigate this risk to the Jason mission, CNES has decided to turn off the Poseidon-2 altimeter on Jason for the duration of the close approaches between Jason and T/P. The period of the altimeter turn off will be from 07-May-2008 at 1752 UTC until approximately 13-May-2008 at 0715 UTC.
DDDuring this period, no Jason OSDR or other science products will be available. The remainder of Cycle 233 will be seriously impacted by science data unavailability. Normal Jason operations will resume in time for Cycle 234, which begins on 13-May at 1328UT.
- The Jason-1 NRT SSHA product will no longer be distributed due to the
degradation of the GPS, which was used to obtain the orbits needed to calculate the SSHA. This does not impact the official Jason-1 science data products, OSDR, IGDR and GDR. If you need SSHA and cannot wait for the GDR or the Jason-1 SSHA product to be released you can calculate the SSHA from the IGDR, which has a 3-5 day time lag. The calculation and editing criteria can be found in the Jason-1 Handbook located at: ftp://podaac.jpl.nasa.gov/pub/sea_surface_height/jason/gdr_b/doc/Handbook_Jason_v3-0.pdf
We apologize for any inconvenience.
PO.DAAC
|
|
Mission
Jason-1 is an input titleimetric mission that measures significant wave height, mean sea surface, sigma0 (which can be converted to wind speed), and all the parameters needed to calculate sea surface height anomalies. It launched December 7, 2001 and began collecting data January 15, 2002 ( cycle 1). As of December 2007, Jason-1 has an orbit accuracy of ~2.5 cm and measures sea surface height with an accuracy of ~3.9 cm. A list of the Jason-1 cycles by date is available at: http://podaac.jpl.nasa.gov/DATA_CATALOG/j1_cyclelist.txt
|
|
| Products |
Data |
S/W |
Validated |
Time Latency |
SWH |
SSHA |
MSS |
Gridded |
# Parameters |
|
| J1 GDR (131) (Ref: Multiple) |
FTP / HEFT |
s/w |
x |
4-6 weeks |
x |
calc |
x |
- |
96 |
Documentation: |
|
Comments: |
Most accurate and detailed product from Jason-1. Does not include SSHA, but this parameter can be calculated per the instructions in the Handbook. |
| |
| J1 SSHA (132) (Ref: Multiple) |
FTP / HEFT |
s/w |
x |
6 weeks |
x |
x |
x |
- |
12 |
Documentation: |
|
Comments: |
SSHA derived from the GDR product.
Data was adjusted to exclude values flagged in the GDR.
|
|
| J1 ATG SSHA (133) (Ref: Multiple) |
FTP / HEFT |
s/w |
x |
6 weeks |
- |
x |
- |
x |
6 |
Documentation: |
|
Comments: |
An along track gridded version of the SSHA |
|
|
FTP / HEFT
NEREIDS |
s/w |
- |
2-3 days |
x |
calc |
x |
- |
96 |
| Documentation: |
|
Comments: |
Similar to GDR. However, data are obtained in near real time and contain fewer corrections. Therefore, this product is less accurate than the GDR and should only be used if the GDR file is not yet available. |
|
|
FTP / HEFT
NEREIDS
|
s/w |
- |
2-3 hr |
x |
- |
- |
- |
24 |
| Documentation: |
|
Comments: |
Near real time data intended for meteorological use. This product has the fewest corrections of the Jason-1 products. |
|
|
Temporal resolution
It takes approximately 10 days for Jason-1 to complete a cycle that surveys the entire Earth. Each cycle consists of 254 passes, which is half an orbit around the Earth and contains ~56 minutes of data. There is ~1 second between measurements.
Spatial resolution
Jason-1 surveys from 66.15° to -66.15°. The along track resolution is 0.0001° in latitude and 0.05° in longitude. A table showing the equator crossing for each pass is available at: ftp://podaac.jpl.nasa.gov/pub/sea_surface_height
/jason/gdr/doc/Handbook_Jason_v3-0.pdf |
|
Documentation
Jason-1 Mission:
http://topex-www.jpl.nasa.gov/mission/jason-1.html
Picot, N., K. Case, S. Desai and P. Vincent, 2006, “AVISO and PODAAC User Handbook.
IGDR and GDR Jason Products”, SMM-MU-M5-OP-13184-CN (AVISO), JPL D-21352 (PODAAC). ftp://podaac.jpl.nasa.gov/pub/sea_surface_height/jason/gdr/doc/Handbook_Jason_v3-0.pdf
Berwin, Robert. W, "PO.DAAC Jason-1 Sea Surface Height Anomaly Product User's Reference Manual"
ftp://podaac.jpl.nasa.gov/pub/sea_surface_height/jason/j1_ssha/doc/j1ssha_manual_v2.html
Berwin, Robert. W. "PO.DAAC Along-Track Gridded Sea Surface Height Anomaly for TOPEX/Poseidon and Jason-1, User's Reference Manual" ftp://podaac.jpl.nasa.gov/pub/sea_surface_height/jason/j1_atg/doc/along_track_gridded_manual_v2.html
|
|
Known Problems and Issues
There are times when the JASON-1 satellite entered safehold-mode, and no data was collected as a result. A list of safing events is available at http://podaac.jpl.nasa.gov/DATA_CATALOG/j1_safehold.txt
The satellite also performed a series of maneuvers to ensure orbital accuracy. A list of maneuvers is available at http://podaac.jpl.nasa.gov/DATA_CATALOG /j1_maneuver.txt
Various conditions, such as heavy rain or ice, may affect input titleimetric measurements. Known environmental and geophysical problems are flagged to allow researchers to easily evaluate these measurements. A description of the Jason-1 flags is available in the Jason-1 IGDR and GDR. ftp://podaac.jpl.nasa.gov/pub/sea_surface_height/jason/gdr/doc/Handbook_Jason_v3-0.pdf
|
|
Frequently Asked Questions
http://podaac.jpl.nasa.gov/FAQ/index.html#altimetry |
|
Citations/References
Menard, Y. and B. Haines, 2001. “Jason-1 CALVAL Plan”, JPL Ref: TP2-J0-PL-974-CN (PO.DAAC).
http://podaac.jpl.nasa.gov/jason/documents/calval4.0.pdf
Vincent, P., M.Ablain, J.Donrandeu, S.Desai, and K.Case. “Jason-1 Calval results”.
http://www.jason.oceanobs.com/html/kiosque/newsletter/news10/vincent_uk.html
Chambers, D.P., J. C. Roes, T.J. Urban. 2003. Calibration and verification of Jason-1 using along-track residual with TOPEX. Marine Geodesy. Vol. 26, no. 3-4, pg. 305-317.
MacMillan, D., Y. Bock, P. Fang, B. Beckely, C. Ma. Calibration of the TOPEX and Jason-1 Altimeter microwave radiometers using VLBI and GPS derived tropospheric delays.
http://sealevel.jpl.nasa.gov/science/invest-macmillan.html
|
|
|
|
|
|
|
|
