Atmospheric Sensing Using GNSS RO - GNSS Remote Sensing: Theory, Methods and Applications - page 152

absorption lines will provide the fundamental thermodynamic variables of the
atmosphere (temperature, pressure, geopotential height, humidity) from near the
surface to the mesopause and ozone concentration through the middle atmosphere
down into the upper troposphere (Kursinski et al. 2002 ; Kirchengast and Schweitzer
2011 ). Another MW band between 500 and 600 GHz (i.e., 0.5-0.6 mm) would
also be quite useful for profiling water vapor and its isotopes in the middle
atmosphere (Kursinski et al. 2002 ).
On the other hand, the LEO-LEO occultation measurements in the short-wave
infrared band (IR-laser occultation at 2-2.5 m) will provide the line-of-sight wind,
greenhouse gases (GHGs) and key chemical species (H 2 O, CO 2 ,CH 4 ,N 2 O, O 3 ,
CO) and four CO 2 and H 2 O isotopes (HDO, H 2 18 O, 13 CO 2 ,C 18 OO) in the upper
troposphere and lower stratosphere. Furthermore, profiles of aerosol extinction,
cloud layering, and turbulence can also be obtained (Kirchengast and Hoeg 2004 ;
Kirchengast and Schweitzer 2011 ).
By directly measurement of water vapor, the LEO-LEO occultation in MW band
is conceived to overcome the wet-dry ambiguity that limits direct interpretation
of the GNSS RO refractivity profiles in the warmer regions of the troposphere
because the wet and dry contributions to refractivity cannot be separated using
refractivity measurements alone. In addition, the higher frequencies used by LEO-
LEO occultation results in negligible ionospheric residual errors and could leads to
highly accurate and independent upper air temperature and water vapor observations
with climate benchmark quality (Kursinski et al. 2009 ).
Such a LEO-LEO occultation (often referred as the “next-generation RO”)
observing system could complement the GNSS RO and provide long-term global
free atmosphere observation (above the boundary layer), which will strongly benefit
the climate community as well as the NWP and atmospheric chemistry communi-
ties. Due to the relatively high cost of building the constellation of the LEO-LEO
occultation observing system, the technique is still in the testing phases. However,
significant support and appreciation of the values of such novel observations have
grown immensely in recent years.
References
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