  The Galactic microquasar GRS 1915+105 shows rich variability which is
categorized into different classes. In this paper, we report temporal and
spectral analysis of GRS 1915+105 to study the properties of the accretion flow
when the light curve is showing $\theta$ class variability. For this purpose,
we use the LAXPC data from the Target of Opportunity observations of India's
first multi-wavelength astronomy satellite AstroSat. The $\theta$ class is
marked by the recurrent appearance of U-shaped regions in the light curve,
where the photon count rate first decreases rapidly and then increases slowly.
For our analysis, we use U-shaped regions of first two orbits (02345 and 02346)
on 2016 March 04. In both of the cases, the dynamic Power Density Spectra (PDS)
showed significant power at around $4-5$ Hz, suggesting the presence of a
low-frequency Quasi-Periodic Oscillation (QPO) around that frequency interval.
The QPO frequency is found to increase with time when the enhancement of the
energy flux also takes place. From the evolution of the spectra, we determine
the evolution of the accretion flow parameters in both of these observations.
Fitting the spectra with the transonic flow solution based Two-Component
Advective Flow (TCAF) model in $4-25$ keV energy band shows that the Keplerian
disk accretion rate rises with the rise in the radiation intensity, while the
location of the centrifugal pressure driven shock front decreases. In both
these data, a gradual increment of power-law photon index with intensity is
observed suggesting the progressive softening of the source.
