MSU Ch 2/3 Daily Lower Troposphere Temps with Limb93 Correction V001 (MSULTT) at GES DISCEntry ID: GES_DISC_MSULTT_V001
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
(MSU) 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
The four MSU channels have contribution functions (CF's) determined by their
wavelength and the atmospheric profile of oxygen. 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 deg C
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.), and diurnal
differences (a.m. vs. p.m.). As a last step, the algorithm screens out known
bad data points found during an exhaustive analysis of the entire data set.
B. MSU Calibration.
The Limb93 Ch 2/3 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). For information on
the calibration procedure, the user is referred to the TOVS MSU Pathfinder
Section 2. MSU LIM93 Data File Structure
The MSU Limb93 data files are given in HDF structure. Every file contains 365
Scientific Data Sets (366 for leap years), one for each day of the year. Each
SDS contains a two dimensional data set, the x dimension is longitude and the y
dimension is latitude. The grid is composed of 144 (longitude) by 72
(latitude) 2.5 by 2.5 degree grid boxes. The first grid box is centered at
78.75 N 178.75 W. The data structure for the SDS data is int16, and the data
are given in hundredth of Kelvin degrees.
Section 3. Algorithm Description
Lower Troposphere Deep Layer Mean Temperature (LTT).
The SDS's contain 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 deg N (S) the footprint data are assigned to adjoining
grid boxes in a weighted method depending on footprint latitude. The data are
intercalibrated to remove differences in the instruments on the different
satellites, differences due to orbit geometries (7:30 a.m. vs 2:30 p.m.
satellites), and diurnal differences (a.m. vs. p.m. orbit). After the a.m. and
p.m. orbits are processed, a horizontal interpolation is used to fill some of
the empty grid boxes.
Data Set Citation
Dataset Title: MSU Ch 2/3 Daily Lower Troposphere Temps with Limb93 Correction
Version: 001Online Resource: http://disc.sci.gsfc.nasa.gov/services/opendap/msu.shtml
Start Date: 1979-01-01Stop Date: 1993-12-31
Latitude Resolution: 2.5 degree
Longitude Resolution: 2.5 degree
Horizontal Resolution Range: 250 km - < 500 km or approximately 2.5 degrees - < 5.0 degrees
Temporal Resolution: Daily
Temporal Resolution Range: Daily - < Weekly
Distribution Media: On-line
Distribution Format: HDF, Binary
Role: TECHNICAL CONTACT
Email: gsfc-help-disc at lists.nasa.gov
Goddard Earth Sciences Data and Information Services Center Code 610.2 NASA Goddard Space Flight Center
Province or State: MD
Postal Code: 20771
Spencer, R.W. and J.R. Christy, 1992a: Precision and radiosonde
validation of satellite grid point temperature anomalies,
Part I: MSU channel 2. J.Climate, 5, 847-857.
Spencer, R.W. and J.R. Christy, 1992b: Precision and radiosonde
... validation of satellite grid point temperature anomalies, Part II: A
tropospheric retrieval and trends 1979-90. J. Climate, 5, 858-866.
Spencer, R.W. and J.R. Christy, 1990: Precise monitoring of global
temperature trends from satellites. Science, 247, 1558-1562.
Creation and Review Dates
DIF Creation Date: 2008-11-12
Last DIF Revision Date: 2009-07-21