Atmospheric Temperature Climate Data Records from Satellite Microwave Sounders - Satellite-based Applications on Climate Change - page 118

N6-NTN N7-N6 N8-N7 N9-N6 N10-N9 N11-N10 N12-N11 N14-N12 N14-N11

1980 1985 1990 1995 2000

Fig. 8.8 Same as Fig. 8.6 but after residual bias correction was applied

on the Earth location (Zou et al. 2009 ). In addition, unevenly sampled satellite
observations in different grid cells will cause sampling-related Earth-location-
dependent biases. To remove these biases, a grid-cell-dependent constant bias
correction was always applied as a final step before merging the satellite data.
This correction ensures that inter-satellite biases at all grid cells tend to zero so that
more reliable regional trends can be obtained from the merged time series.

8.3.6 Frequency Differences Between MSU and AMSU Channels

The MSU is a 4-channel instrument, while AMSU-A has 15 channels. The AMSU
channels 5, 7, and 9 are the equivalent channels for the MSU channel 2, 3, and 4, but
with slightly different channel frequencies. These frequency differences cause a
temperature difference on the order of 2-5 K between MSU and AMSU-A
observations since they observe different layers of the atmosphere. Depending on
atmospheric lapse rate climatology, these temperature differences also vary with
seasons, geographic locations, and channels (Iacovazzi et al. 2009 ; Zou and Wang
2011 ). To reduce these type of biases, yearly mean monthly bias statistics between
MSU and AMSU-A are derived for each of their equivalent channels and grid cells.
These biases are then subtracted from the monthly AMSU-A data, so that they
become MSU equivalent channel observations.

8.3.7 Well-Merged NOAA Version 2.0 MSU/AMSU Atmospheric
Temperature TCDR

With instrument calibration and bias correction approaches as described above,
version 2.0 of a climate-quality, 34-year (1979-present) MSU/AMSU atmospheric
temperature TCDR has been generated at NOAA/NESDIS. This is a global gridded
dataset with 2.5 latitude by 2.5 longitude grid resolution. Both monthly and
pentad data are available. The TCDR includes temperature mid-troposphere
(TMT, MSU channel 2 merged with AMSU-A channel 5), temperature tropopause
and stratosphere (TTS, MSU channel 3 merged with AMSU-A channel 7; also