  We present the detection and characterisation of mesoscale waves on the lower
clouds of Venus using images from the Visible Infrared Thermal Imaging
Spectrometer onboard the European Venus Express space mission and from the 2
$\mu$m camera (IR2) instrument onboard the Japanese space mission Akatsuki. We
used image navigation and processing techniques based on contrast enhancement
and geometrical projections to characterise morphological properties of the
detected waves, such as horizontal wavelength and the relative optical
thickness drop between crests and troughs. Additionally, we performed phase
velocity and trajectory tracking of wave packets. We combined these
observations to derive other properties of the waves such as the vertical
wavelength of detected packets. Our observations include 13 months of data from
August 2007 to October 2008, and the entire available data set of IR2 from
January to November 2016.We characterised almost 300 wave packets across more
than 5500 images over a broad region of the globe of Venus. Our results show a
wide range of properties and are not only consistent with previous observations
but also expand upon them, taking advantage of two instruments that target the
same cloud layer of Venus across multiple periods. In general, waves observed
on the nightside lower cloud are of a larger scale than the gravity waves
reported in the upper cloud. This paper is intended to provide a more in-depth
view of atmospheric gravity waves on the lower cloud and enable follow-up works
on their influence in the general circulation of Venus.
