The National MST Radar Facility at Gadanki near Thirupati, under the Department
of Space, has set up a Sodium Lidar, which is a ground based instrument for
studying vertical and temporal structure of mesosphere and lower thermosphere
(MLT) region. This is the first of its kind in India and will help in
characterising the wind and wave induced sodium density. The first observation
from the new Sodium Lidar was made on January 10, 2005.
The occurrence of sporadic layers of neutral sodium and other metals at around
100 km heights is a phenomenon that is both interesting and puzzling. The
shooting meteors are the genesis for the formation of atmospheric metal layers.
As meteors enter the atmosphere, they burn-up or ablate and leave debris in
their path. This ablation occurs near altitudes of 80 to100 km. Part of this
debris is neutral metal atoms and ions such as sodium, iron, potassium and
calcium, which exist in this unique region as the air is thin for them to be
trapped in compounds with oxygen but too thick to allow ionisation of all the
neutral atoms into ions. This region of the atmosphere also hosts the airglow
layers. Metal atoms are useful for remote sensing as they are shiny at specific
resonant wavelengths. For atmospheric sodium this resonant wavelength is 589
nm, which appears as bright orange. Atmospheric sodium layer acts as tracers of
winds and waves in this region.
National MST Radar Facility is one of the prime centers for advanced research in
atmospheric sciences. In addition to the state of art
Mesosphere-Stratosphere-Troposphere (MST) radar, it has facilities such as the
Lower Atmospheric Wind Profiler and Rayleigh/Mie Lidar. Very recently, Raman
Lidar and Boundary Layer Lidar were set up. These facilities complement and
supplement the MST radar for an integrated and comprehensive study of lower,
middle and upper atmosphere.
Sodium Lidar has further enhanced the scope of atmospheric research at this