TOVS Pathfinder C1 MSU Pentad am (Ch 2/3, Ch 4, Ocean Precip)
Entry ID:
msuc1penam
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Summary
Abstract:
Section 1. General Description Spencer and Christy (1990) demonstrated that accurate estimates of global atmospheric temperatures could be derived from the Microwave Sounding Units flown on NOAA's TIROS-N series of satellites. The MSU's have been continuously operating for more than 14 years collecting measurements of the thermal emission of radiation by ... molecular oxygen at four frequencies near 60 GHz. The four MSU channels have contribution functions (CF's) determined by their wavelength and the atmospheric profile of oxygen. The CF's for the four channels peak succeedingly higher in the atmosphere. MSU channel 1 has a CF peak near the surface, and is influenced strongly by temperature and liquid water near the surface. The channel 2 CF is dominated by a wide peak near 50 kPa. Channel 3 peaks near the tropopause (25 kPa) and the Channel 4 CF has a somewhat sharper peak in the lower stratosphere (7 kPa). Spencer and Christy (1992 a,b) demonstrated that the MSU calibrations have been very stable, with a precision of monthly satellite measurements of 0.01 degrees Celcius for the global mean. A. 2/3 Lower Tropospheric Retrieval. Spencer has developed a procedure for removing the stratospheric influence in channel 2 using data from MSU channel 3. The use of channel 3 allows for a different retrieval at each footprint producing a robust temperature estimate suitable for daily grid point analysis. His algorithm (2/3 retrieval) uses a linear combination of channels 2 and 3 to produce a CF with a peak in the lower troposphere near 60 kPa. The retrieval is constrained to reduce the influence of calibration drifts in channel 3 on several MSU instruments. The 2/3 retrieval algorithm screens the data to remove calibration differences between satellites along with the effects of precipitation size ice particles, and corrects for the effect of changing earth incidence-angle across a scan line (Limb93). The data have been inter calibrated to correct for differences between local orbit crossing times (e.g., 2:30 a.m. vs. 7:30 a.m.); however, the ascending and descending orbits have been processed separately. As a last step, the algorithm screens out known bad data points found during an exhaustive analysis of the entire data set. B. Ch 4 Lower Stratospheric Retrieval. Spencer and Christy (1993) developed a deep-layer lower stratospheric temperature retrieval using MSU channel 4. The MSU channel 4 CF lies nearly entirely in the stratosphere with a peak near 7 kPa. They validated their 2.5 degree grid point data against rawinsondes, finding correlation's with single-station data as high as .99. The stratospheric retrieval corrects the channel 4 data for scan angle differences across the scan line (Limb93), and removes known bad scan lines. The data have been inter calibrated to remove calibration differences between satellites and to correct for differences between local orbit crossing times (e.g., 2:30 a.m. vs. 7:30 a.m.). However, the ascending and descending orbits have been processed separately. C. Oceanic Precipitation Data set. The oceanic precipitation estimates follow the method of Spencer (1993). Oceanic precipitation is estimated by increased warming in MSU channel 1 over a threshold. The increased warming is attributable to emission by liquid water in the lower troposphere. Warming due to air mass differences are removed using information from the MSU channel 2/3 retrieval. The precipitation estimate has been calibrated into mm per day rainfall using eight years of rain gauge data from tropical island locations. A climatological ice mask has been used to screen out anomalous precipitation over ice covered ocean. Likewise, the maximum value allowed has been set at 99.9 mm/day to further screen out any remaining ice influence. Also, because this method only works in the Tropics and mid-latitudes, the retrieval is only calculated for latifudes 60 S to 60 N. Spencer (1993) discusses the calibration and demonstrates there is good agreement between the MSU precipitation estimates and previous climate rainfall data sets. Because the algorithm methodology uses all orbits in a 24 hour period to calculate the rainfall estimate, no diurnal information is available in this data set. D. MSU Calibration. All the Pathfinder C1 retrievals use calibrated MSU data. The MSU brightness temperatures for all four channels were linearly calibrated using the radiometric counts measured viewing the earth scene as compared to the difference between the radiometric measurement while viewing a warm calibration load and a similar view of deep space (assumed to be 2.5K). Section 2. TOVS Pathfinder C1 Data File Structure This file contains data from the a.m. orbits for a single five day pentad period. Morning (a.m.) orbits for five days were averaged to create the pentad dataset. The grid point standard deviations and count parameters were also averaged resulting in an average daily grid point standard deviation. The pentad data product file contains data for seven TOVS level 3 geophysical parameters given in separate scientific data sets (SDS's) in HDF format. The first scientific data set in each file contains the lower troposphere deep-layer mean temperature (Ch 2/3) estimate derived using Spencer's retrieval method. The second SDS contains the lower stratosphere (Ch 4) deep-layer mean temperature estimate (Spencer and Christy, 1993) and the third SDS, the oceanic precipitation estimates from MSU (Spencer 1993). The next two SDS's (four and five) contain the grid point standard deviations for the Ch 2/3 and Ch 4 parameters, while the last two (six and seven) contain the grid point sample count parameter for the Ch 2/3 and Ch 4 products. The data sets have been processed by the Observing Systems Branch of the Space Science Laboratory at NASA/MSFC, using the algorithms described in Section 3 (for complete details of the processing algorithms the user is referred to the TOVS Pathfinder C1 User's Guide or the references listed in Section 4. The standard deviation and counts provided in the Path C1 data files are calculated from data for all the footprints assigned to each grid box. Details of the grid box assignment and weighting are discussed in the TOVS Pathfinder C1 User's Guide. The counts and standard deviations are provided for the two deep-layer temperature products, but not for the oceanic precipitation. Section 3 Algorithm Description A. Lower Troposphere Deep Layer Mean Temperature. SDS 1 contains the lower tropospheric temperature parameter (Ch 2/3) which is derived using a linear combination of MSU channels 2 and 3: 2/3 Tb = 1.6 * Tb2 - .6 * Tb3 where, Tb2 refers to the brightness temperature in MSU channel 2 and Tb3 the brightness temperature in MSU channel 3 The 2/3 retrieval is calculated for each footprint of the MSU scan line, the latitude and longitude of the footprint are calculated and the appropriate limb correction (Limb93) is applied based on latitude, longitude, month, and scan angle. Next, the footprint data are assigned to the appropriate grid box. North (south) of 66.7 degrees N (S) the footprint data are assigned to adjoining grid boxes in a weighted method depending on footprint latitude. After all the a.m. orbits are processed, a horizontal averaging is used to fill some of the empty grid boxes. Once the final 2.5 degree grid is completed, the data are resampled at a 1 degree grid spacing. B. Lower Stratosphere Deep Layer Mean Temperature. The lower stratospheric temperature (Ch 4) is given in SDS 2. The stratospheric temperature retrieved is simply the black body temperature linearly calibrated from the radiometric counts in MSU channel 4 at each footprint. The stratospheric retrieval is calculated for each footprint of the MSU scan line, the latitude and longitude of the footprint are calculated and the appropriate limb correction (Limb93) is applied based on latitude, longitude, month, and scan angle. Next, the footprint data are assigned to the appropriate grid box. North (south) of 66.7 degrees N (S) the footprint data are assigned to adjoining grid boxes in a weighted method depending on footprint latitude. After all the a.m. orbits are processed, a horizontal averaging is used to fill some of the empty grid boxes. When the final 2.5 grid is completed, the data are resampled at a 1 degree grid spacing. C. Oceanic Precipitation. The methodology used to calculate the oceanic precipitation is highlighted in Section 1 C. For a more in-depth discussion the reader is referred to Spencer (1993). Because of the algorithm design, the a.m. and p.m. orbits are not separated, but are combined into a daily rainfall estimate, so no analysis of a diurnal effect is possible. Likewise, because of the algorithm design, the standard deviations and grid box counts are not available for this product. The precipitation estimates are calculated on a 2.5 degree grid (for latitudes 60 S to 60 N) and are resampled onto the 1 degree grid. The Path C1 data files contain the precipitation estimates on the 1 degree grid, with the same rainfall product provided in both the a.m. and p.m. data files.
Geographic Coverage
(Click for Interactive Map)
Spatial coordinates
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N: 89.0
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S: -89.0
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E: 180.0
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W: -180.0
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Data Set Citation
Dataset Originator/Creator:
J. B. Blair, M. A. Hofton, and D. L. Rabine.
Dataset Title:
Processing of NASA LVIS elevation and canopy (LGE, LCE and LGW) data products
Dataset Release Date:
2006
Dataset Publisher:
Code 698 NASA Goddard Space Flight Center.
Version:
1.01
Online Resource:
http://lvis.gsfc.nasa.gov
Temporal Coverage
Start Date:
2005-01-01
Stop Date:
2005-01-01
Access Constraints
While substantial efforts have been made to ensure the accuracy of data and documentation, complete accuracy of data sets can not be guaranteed. All data are made available "as is". The LVIS team can not assume responsibility for damages resulting from mis-use or mis-interpretation of datasets or from errors or omissions that may exist in the data. Data users are welcome to collaborate with the ... LVIS team, as this may minimize the potential for misinterpretation of the data. In order to develop an active community and ensure the flow of ideas between interested parties, the LVIS team makes the following suggestions of individuals who download LVIS data: - On projects that are integrally dependent on LVIS data, you have the option to request collaboration and/or co-authorship from the LVIS team. (NOTE: This is in no way binding. You are free to use the data on your own. You are not expected or required to contact or work with us in any way. This is simply a suggestion.) - Please acknowledge the source of the data set as the LVIS team/ project and the appropriate NASA Grant numbers responsible for funding these data sets in any publications using these data and documentation (see LVIS Citations) - Consider notifying (a simple email will suffice) the LVIS Principal Investigator when any derivative work based on or derived from the data and/or documentation is distributed or presented. (We always appreciate when our data is used and helps result in scientific publications.) - When derivatives of the LVIS data are distributed in any way, notify subsequent users that such derivative work is not the original LVIS data and/or documentation distributed on the LVIS web site - Do not redistribute original data and documentation yourself, instead please direct individuals to http://lvis.gsfc.nasa.gov. It is important that we have the ability to contact users of LVIS data so that we can notify them when we upload new data sets and/or correct mistakes in the existing data sets. - If you would like to share your work with us, we would greatly appreciate it if you would notify us and/or send a reprint of any publications resulting from the use of the data and/or documentation. 
Use Constraints
See data use at the project home page.
Data Set Progress
COMPLETE
Personnel
Role:
TECHNICAL CONTACT
Phone:
301-614-6741
Email:
James.B.Blair at nasa.gov
Contact Address:
NASA
Goddard Space Flight Center
Mailstop 694.0
City:
Greenbelt
Province or State:
MD
Postal Code:
20771
Country:
USA
Role:
DIF AUTHOR
Phone:
(301) 614-6898
Fax:
301-614-5268
Email:
Tyler.B.Stevens at nasa.gov
Contact Address:
NASA Goddard Space Flight Center
Global Change Master Directory
City:
Greenbelt
Province or State:
MD
Postal Code:
20771
Country:
USA
Publications/References
Blair, J. B., D. L. Rabine, and M. A. Hofton. 1999. The Laser Vegetation Imaging Sensor: a medium-altitude, difitisation-only, airborne laser altimeter for mapping vegetation and topography. ISPRS Journal of Photogrammetry & Remote Sensing. 54: 115-122.
Creation and Review Dates
DIF Creation Date:
2007-09-26
Last DIF Revision Date:
2012-08-22
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