Studies on the Impacts of 3D-VAR Assimilation of Satellite Observations on the Simulation of Monsoon Depressions over India - Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications - page 638

National Oceanic and Atmospheric Administration (NOAA)-KLM satellite series.
The ATOVS sensor comprises of the Advanced Microwave Sounding Units A and
B (AMSU-A, AMSU-B), and the High Resolution Infrared Radiation Sounder
(HIRS/3). The NOAA-TOVS has three infrared channels at 8.3, 7.3, and

m
and can provide moisture information for the following three layers: 1,000-700 hPa,
700-500 hPa, and 500-300 hPa. The variable scale-height algorithm is used to
derive the vertical humidity profile at standard levels 1,000, 850, 700, 500, 400
and 300 hPa from the precipitable water vapor in the three layers. The method and
its validation are outlined in Rajan et al. ( 2002 ). Rajan et al. ( 2002 ) found that the
associated root mean square error (RMSE) when validated against near radiosonde
observations was less than 10 %. The temperature sounding data used in this study
are from the HIRS/2 instrument onboard TOVS. TOVS satellite makes a morning
and an evening pass (around 7:30 A.M. and 7:30 P.M. Indian Standard Time) over
the Indian subcontinent. Hence, the TOVS temperature and humidity profiles are
ingested at the nearest analysis time, i.e., at 00 and 12 UTC.
ATOVS data archived in the NOAA Comprehensive Large Array Stewardship
system (CLASS) is available in the raw Level 1b format. The ATOVS data has
been quality controlled, and assembled into discrete data sets, and to which the
calibration information as well as the information of location on Earth are appended.
This Sounding and Imager Data from the High Resolution Picture Transmission
(HRPT) direct read out stream of NOAA-ATOVS satellite is processed end-to-
end using the ATOVS and AVHRR (Advanced Very High Resolution Radiometer)
Processing Package (AAPP). The output of AAPP is called the Level 1d data,
in which factors such as instrument reflectance and/or brightness temperatures
are mapped on a common instrument grid (HIRS in this study) with navigation,
calibration and contamination information appended. This Level 1d data is then fed
to the International ATOVS Processing Package (IAPP); to retrieve bias corrected
parameters for assimilation. The data has a horizontal resolution of about 42 km
and gives temperature and humidity sounding in 42 vertical levels, up to 10 hPa
level. Satellite data observed and pre-processed in the time window of ˙ 1:5

6:7

h
from the assimilation time are ingested. English et al. ( 2000 ) investigated the impact
of assimilating ATOVS data in a numerical weather prediction (NWP) model, and
concluded that the information provided by the radiance observations reduced the
forecast errors by about 20 % in the southern hemisphere and by about 5 % in the
northern hemisphere.

to ˙ 2

26.2.3.4 Moderate Resolution Imaging Spectroradiometer (MODIS)

The “Moderate Resolution Imaging Spectroradiometer” (MODIS) is a key instru-
ment onboard the Terra and Aqua satellites launched in 1999 and 2002, respectively.
Both Terra MODIS and Aqua MODIS are viewing the entire Earth's surface every
1-2 days, acquiring data over several wavelengths in two important regions of the
electromagnetic spectrum, namely the near-infrared (NIR) and the infrared (IR)