|Corrected Earth Probe Data|
|correction basis: NOAA-16 SBUV/2 ozone
time period: August 1996 - December 13, 2005
data products corrected: ozone, reflectivity
By mid-2000, the Earth Probe (EP) TOMS instrument degradation became so large that standard correction procedures could no longer produce accurate ozone. The problem is believed to be inhomogeneous degradation of the scanner mirror on TOMS that results in a calibration error that is different at different latitudes. We have warned users that the production EP ozone data should NOT be used for trend analysis.
We have now applied a correction to the Earth Probe data that stabilizes the EP ozone record. This empirical correction is based on the NOAA-16 SBUV/2 ozone record, with a solar zenith angle dependence that accounts for much of the spurious latitude dependence observed in the current data. Only the ozone and reflectivity records have been corrected. The aerosol index data and SO2 records are more complex and have not been corrected by this empirical correction.
Comparison with the ground network shows that the resulting ozone is stable within ± 1% over the 1996-2005 period. In the period 2002-2005 in the northern hemisphere, there is a residual seasonally-dependent error of ± 1.5% magnitude. These data should still NOT be used as a source for trend analysis since they are no longer independent.
The existing Earth Probe ozone and reflectivity data and images were replaced by the corrected Earth Probe ozone and reflectivity data and images on September 4, 2007. The corrected data and images are available on this web site and anonymous ftp site (ftp://toms.gsfc.nasa.gov/pub/eptoms) at the same locations as the previous data.
|Earth Probe TOMS Deactivated|
|Following the transmitter failure on December 2, 2006, all attempts to revive Earth Probe TOMS failed. Even though the TOMS instrument itself was still working as far as we know, with no way to send data to the ground, there was no point in continuing to operate the spacecraft.
After careful review, on May 30, 2007, commands were sent to Earth Probe to deactivate all satellite systems. Subsequent radar scans showed that Earth Probe went from sun-pointing safehold configuration to a slow tumble, confirming that the deactivation commands executed.
|Earth Probe TOMS to be turned off|
|On December 2, 2006, contact with the Earth Probe spacecraft was lost. Tests confirmed that the transmitter had failed but that the receiver still worked. Presumably TOMS still works, but with no way to bring the data down, there is no point in continuing to operate the spacecraft. The decision has been made to power down the spacecraft late this spring. Since there is no more on-board fuel, it is not possible to do a controlled re-entry. But at its altitude of 730 km., it will be decades before Earth Probe re-enters the atmosphere.
EP was designed as a two-year mission. At launch, we guessed that five years was its maximum likely lifetime. Instead, EP returned more than ten years of ozone data. It was a VERY successful mission!
|TOMS Science and Data Processing Team receives the 2006 William T. Pecora Award|
|The TOMS Science and Data Processing Team was presented the 2006 William T. Pecora Award on Wednesday evening, December 13, 2006 at the American Geophysical Union (AGU) conference in San Francisco, CA. The William T. Pecora Award is presented annually to individuals or groups that make outstanding contributions toward understanding the Earth by means of remote sensing. The award is sponsored jointly by the Department of the Interior (DOI) and the National Aeronautics and Space Administration (NASA). The award was established in 1974 to honor the memory of Dr. William T. Pecora, former Director of the U.S. Geological Survey and Under Secretary, Department of the Interior. Dr. Pecora was a motivating force behind the establishment of a program for civil remote sensing of the Earth from space. His early vision and support helped establish what we know today as the Landsat satellite program. The award consists of a citation and plaque, which are presented to the recipient at an appropriate public forum by the Secretary of the Interior and the NASA Administrator or their representatives. The name of the recipient is also inscribed on permanent plaques, which are displayed by the sponsoring agencies.|
|Earth Probe TOMS in safehold|
|On Saturday, December 2, 2006, contact with Earth Probe was lost. There has been no communication with the spacecraft since. NORAD was able to confirm that the spacecraft was intact and Earth-oriented, which tell us that it is still operational and maintaining attitude. On Wednesday December 6 the spacecraft was commanded to go to SAFE mode, in which it points at the sun, which will maintain power indefinitely. NORAD verified that the spacecraft responded and is now sun-pointing. This indicates that the receiver and processor are working. Earth Probe has been operating on its backup transmitter since 1998 when the primary failed. The operations team tried switching to the zenith antenna in hopes that the problem was the nadir antenna, but still no signal was received. This likely means that the transmitter has failed. At this point the probability of recovering looks poor, but we are still trying.|
|Google Earth comes to OMI|
|OMI Aerosols now in Google Earth!|
|Aura Top 10 Discoveries|
|Approaching its second anniversary since launching in July 2004, Aura has been retrieving information and producing valuable data of the Earth and its atmospheric properties. Each instrument working individually and alongside its counterparts to bring us ozone measurements, tropospheric maps of carbon monoxide and cloud ice, as well as measurements in the stratosphere.|
|Discontinued Near Real Time Earth Probe TOMS Data|
|In view of the good performance of OMI and the calibration problems with EP TOMS, we have discontinued offering near real time Earth Probe TOMS data beginning January 1, 2006. Within a few days we will offer access to the OMI data via the current web page and tools. Later this spring we will make this an Ozone Mapping web page rather than a TOMS web page, since we are moving to an era that is data centric rather than instrument centric.|
|TOMS Calibration Error:|
|The Version 8 algorithm is now used for all TOMS data. For data beginning in year 2000, the calibration has been stabilized relative to NOAA-16 SBUV/2 in the equatorial zone. Because of continuing changes in the optical properties of the front scan mirror that are not well understood, we are now seeing a latitude dependent error that cannot be corrected by a simple calibration correction. The calibration appears to be stable near the equator. But by 50 degrees latitude, there is now a -2% to -4% error in TOMS, a bit larger in the northern hemisphere than in the southern hemisphere. Because of this error, data since 2002 should NOT be used for trend analysis.|
|Version 8 data of TOMS now available|
|Version 8 data and products of the TOMS processing algorithm are now here and available for the Nimbus-7 and Earth Probe instruments. For more information and updates of Version 8 of the TOMS processing algorithm, see the Version 8 update web page. Note that all data and product references below this update (i.e. prior to 23 August 2004) display Version 7 data and products.|
|Earth Probe error in attitude|
|Early on November 27, 2003, the Earth Probe spacecraft detected what appeared to be a large error in attitude (pitch) and went into safehold, shutting down the instrument and orienting to conserve power. This appears to be identical to what happened in May of this year. We hope to have TOMS operating in a nominal science mode some time during the week of December 1, 2003.|
|The TOMS instrument has been fairly stable|
|The TOMS instrument has been fairly stable for the past year. Comparison with the Brewer instrument at Goddard shows that the current calibration is fairly good - TOMS ozone is about 3% higher than the Brewer. Beginning August 1, 2003, we implemented another correction to remove scan angle dependence, but this time the error was small even before correction.|
|Spacecraft in safehold|
|Early on May 15 the spacecraft detected what appeared to be a large error in attitude (pitch) and went into safehold - shutting down the instrument and orienting to conserve power. This appears to be identical to what happened last August, so we are now trying to understand the source of the problem before turning the instrument back on. We had thought that it was a Single Event Upset - a high energy particle affecting a memory location - but the events are too similar to be coincidence. We hope to have TOMS operating again early next week.|