Privacy Policy and Important Notices
Updated: Friday, 19-Jun-2009 11:44:38 EDT
To assist in your cruise planning, we can
inform you of when the various operational
ocean color sensors will be viewing given
latitude/longitude locations on particular
dates or within a range of dates. Currently,
the sensors include: SeaWiFS, MODIS,
OCI, OCM, OSMI & MERIS.
Uncertainty in the predicted satellite ephemeris
is thought to be approximately 30 seconds
in equator crossing time when predicted one
month in advance, which translates to approximately
200 km uncertainty in satellite location
at the times given. The uncertainty decreases
with shorter prediction intervals, of course.
Your predictions will be sent to you via email. To provide services to you in a timely manner, we need to obtain your cruise schedule as soon as possible (you may update your cruise information with us later if necessary). Please use our On-line form or you may submit your request via email to schedule@oceancolor.gsfc.nasa.gov.
The SeaWiFS field of view is nominally 1.6 mRads, and its side-to-side scan angle is +/- 58.3 degrees. The instrument is tilted either 20 degrees forward or aft relative to the satellite's direction of motion. Elevation angles at a particular location may be less than 30 degrees (i.e. the zenith angle will be greater than 60 degrees) due to the large scan angle, the 20 degree tilt, and the curvature of the earth. Viewing at elevation angles of less than 45 degrees will result in an atmospheric path length which is too large for accurate radiometry, so useful data will occur only when the elevation angle is greater than 45 degrees. Note that even if the satellite passes directly overhead, the resulting elevation angle will be 70 degrees due to the 20 degree tilt. See http://oceancolor.gsfc.nasa.gov/SeaWiFS/SEASTAR/SPACECRAFT.html for a more complete description of the SeaWiFS sensor.
The tilt times of the SeaWiFS sensor are given definitely by SeaWiFS Mission Control approximately one week in advance of the current date. The tilt is changed so that the sensor does not look into the sun, but the exact times at which the change is commanded vary slightly so as to ensure complete coverage. For predictions made for dates after the last commanded tilt time that we have, we assume the tilt to occur at the subsolar point.
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SeaWiFS: Viewing Times
* 1 = tilt in progress; 2 = tilt schedule unknown, estimated tilt
3 = Sat. view ang. > 45 deg; 4 = Possible sunglint
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Date Time Lat Lon Sat. Sat. Range Sun Sun Tilt Flags*
(UTC) (DEG) (DEG) Azi. Elev. (km) Azi. Elev.
--------------------------------------------------------------------------------
13 Mar 2000 10:34:52 45.314 12.508 105.58 19.33 1637 165.20 40.98 AFT 3
13 Mar 2000 12:12:47 45.314 12.508 262.97 45.86 950 197.67 40.56 AFT
14 Mar 2000 11:18:34 45.314 12.508 127.69 47.11 933 179.82 42.39 AFT
14 Mar 2000 12:56:06 45.314 12.508 284.13 20.19 1601 211.27 37.77 AFT 3
15 Mar 2000 10:24:06 45.314 12.508 102.72 15.34 1839 161.68 41.23 AFT 3
15 Mar 2000 12:02:05 45.314 12.508 249.46 56.10 840 194.57 41.83 AFT
16 Mar 2000 11:07:49 45.314 12.508 119.04 37.84 1077 176.33 43.12 AFT
16 Mar 2000 12:45:27 45.314 12.508 280.74 24.60 1426 208.61 39.40 AFT 3
The range given is the line of sight distance
between the sensor and the ground location,
not the great circle distance between the
sub-satellite point and the ground location.
Two versions of the MODIS instrument are in operation. One aboard the Terra satellite (~10:30am equatorial crossing time, descending node), and one aboard the Aqua satellite (~1:30pm equatorial crossing time, ascending node).
The MODIS side-to-side scan angle is +/-
55 degrees. The instrument is nadir pointing.
Predictions generated for MODIS are optimized
for ocean color, therefore by default do not include
times when the sensor would view a location
on the dark side of the earth. Night time predictions are available, just
add a note in the comments section when making the request.
See http://modis.gsfc.nasa.gov/ for a more complete description of the MODIS
sensor.
The MERIS Field-of-view is 68.5 degrees. The instrument is nadir pointing. See http://envisat.esa.int/ for a more complete description of the MERIS sensor.
The MOS-B field of view is nominally .094 degrees, and its side-to-side scan angle is +/- 7 degrees. See the MOS home page http://www.ba.dlr.de/NE-WS/ws5/index_mos.html for a more complete description of the MOS-B sensor.
The OCI field of view is nominally 60 degrees. See the OCI home page http://www.oci.ntou.edu.tw/ for a more complete description of the OCI sensor.
The KOMPSAT-1 OSMI is designed to provide worldwide ocean color data from a 685km sun synchronous orbit. The orbit crossing time is 10:50 AM and the inclination is 98.13 degrees. The OSMI instrument performs whisky-broom scan imaging operation with a cross-track ground swath of 800 km. The ground track re-visit time is 28 days. The field of view is nominally 17 degrees, the side-to-side scan angle is +/- 29.75 degrees. The OSMI instrument is designed to perform imaging operation for 20% per orbit. See the KOMPSAT-1 homepage http://kompsat.kari.re.kr/english/index.asp for a more complete description of the OSMI sensor.
The OCM field of view is +/- 43 degrees. It has a swath width of 1420 km. See the IRS-P4 home page for a more complete description of the OCM sensor. The OCM sensor has the capability to tilt +/- 20 degrees in 5 degree increments to avoid sun glint contamination. Since the OBPG project does not have access to the OCM command schedules, we estimate full tilt transition at the subsolar point
================================================================================
MODIS: Viewing Times
* 1 = tilt in progress; 2 = tilt schedule unknown, estimated tilt
3 = Sat. view ang. > 45 deg; 4 = Possible sunglint
================================================================================
Date Time Lat Lon Sat. Sat. Range Sun Sun Tilt Flags*
(UTC) (DEG) (DEG) Azi. Elev. (km) Azi. Elev.
--------------------------------------------------------------------------------
13 Mar 2000 10:00:11 45.314 12.508 99.02 48.48 915 154.61 36.88 NADIR
14 Mar 2000 10:42:58 45.314 12.508 287.64 66.28 769 167.85 41.31 NADIR
15 Mar 2000 09:47:53 45.314 12.508 96.99 36.99 1092 150.45 38.24 NADIR
15 Mar 2000 11:25:29 45.314 12.508 294.89 27.35 1333 182.26 42.76 NADIR 3
16 Mar 2000 10:30:44 45.314 12.508 289.28 86.00 713 163.84 41.58 NADIR
The range given is the line of sight distance
between the sensor and the ground location,
not the great circle distance between the
sub-satellite point and the ground location.
Privacy Policy and Important Notices
Updated: Friday, 19-Jun-2009 11:44:38 EDT