  The North American Nanohertz Observatory for Gravitational Waves (NANOGrav)
project has the primary goal of detecting and characterizing low-frequency
gravitational waves through high-precision pulsar timing. The mitigation of
interstellar effects is crucial to achieve the necessary precision for
gravitational wave detection. Effects like dispersion and scattering are more
influential at lower observing frequencies, with the variation of these
quantities over week-month timescales requiring high-cadence multi-frequency
observations for pulsar timing projects. In this work, we utilize the
dual-frequency observing capability of the Giant Metrewave Radio Telescope
(GMRT) and evaluate the potential decrease in dispersion measure (DM)
uncertainties when combined with existing pulsar timing array data. We present
the timing analysis for four millisecond pulsars observed with the GMRT
simultaneously at 322 and 607 MHz, and compare the DM measurements with those
obtained through NANOGrav observations with the Green Bank Telescope (GBT) and
Arecibo Observatory at 1400 to 2300 MHz frequencies. Measured DM values with
the GMRT and NANOGrav program show significant offsets for some pulsars, which
could be caused by pulse profile evolution in the two frequency bands. In
comparison to the predicted DM uncertainties when incorporating these
low-frequency data into the NANOGrav dataset, we find that higher-precision
GMRT data is necessary to provide improved DM measurements. Through the
detection and analysis of pulse profile baseline ripple in data on test pulsar
B1929+10, we find that, while not important for this data, it may be relevant
for other timing datasets. We discuss the possible advantages and challenges of
incorporating GMRT data into NANOGrav and International Pulsar Timing Array
datasets.
