# Probing Dust and Water in Martian Atmosphere with Far-Infrared Frequency Spacecraft Occultation
## 1 Introduction
Some important observations are associated with the vertical structure of the ionosphere under various space weather conditions [27; 28], and investigate the lower atmosphere for trends in gravity wave activity [29] and CO\({}_{2}\) condensation at the poles [30]. Radio occultation observations can resolve temperatures at the planetary boundary layer (PBL) to understand convective activity and the influence of surface processes and topography on atmospheric dynamics. Past radio occultations have determined the depth of the convective boundary layer and its spatial variation by resolving the temperature structure within the lowest scale height in the atmosphere [31; 32]. Infrared retrievals have coarse vertical resolutions of about 10-15 km for TES [5] and 5 km for MCS [18] and CRISM [20] compared to radio science experiments that provide vertical resolutions up to 1 km above 20 km altitude and \(\sim\)100 m resolution below 20 km. Infrared (IR) spectrometers are limited by the width of the weighting functions at the wavelengths of the observation. On the other hand, the vertical resolution of radio science is limited by diffraction to the order of the first Fresnel zone diameter. Moreover, algorithms based on small-scale diffraction theory [33] and the radio holographic method [34] overcome the limitation of vertical resolution by diffraction in radio occultations and provide a significant improvement in measurements of temperature and dust profiles in the planetary boundary layer. The effect of dust in climate models could also be implemented using data assimilation [35]. The lower density of Mars' atmosphere and the lack of oceans pose significant challenges for data assimilation. The radiative time scale of Mars is much shorter than that of Earth and Mars is affected more strongly by the presence of dust aerosols. The assimilation of dust, temperature, and water would improve predictions of synoptic-scale events with GCMs. However, the coarse resolution of currently available temperature and dust opacity data does not provide enough information about the planetary boundary layer. To accurately simulate dust activity, high-resolution data on dust opacity and temperatures are required both in terms of vertical resolution [36] and spatial coverage. Mars exhibits global-scale structures in dust storms which can be resolved by improving spatial coverage and monitoring them for long durations [37]. Currently, radio occultation retrievals of atmospheric temperature profiles provide the highest resolution data required for data assimilation purposes [22; 38]. Amplitude data from the radio occultation of Venus has been used to retrieve the concentration of cloud-forming vapors like SO\({}_{2}\), and H\({}_{2}\)SO\({}_{4}\)[39; 40]. Radio science experiments on Venus have been used to retrieve SO\({}_{2}\) and H\({}_{2}\)SO\({}_{4}\) vapor concentrations, which help us understand the role of meridional circulation in cloud transport [40]. However, Mars radio occultation experiments from previous missions show that the observations are not sensitive to dust, and any signal loss due to Martian dust has not been reported. The average size of Martian dust particles ranges from 1 to 2 \(\mu\)m [41; 42]. Therefore, higher frequency bands with wavelengths of the order of dust size will experience signal loss due to dust activity, which can be recorded in amplitude measurements. It should be noted that spacecraft occultation allows the signal to cover long distances in the atmosphere. Hence, the wavelength of the transmitted signal will need to be larger than the dust size to avoid complete attenuation of the signal, i.e., 30-300 \(\mu\)m.  
In recent years, the interest in the application of THz technology for Earth and Mars has increased significantly [43; 44; 45; 46]. Key applications include satellite telecommunications and remote sensing of trace gases. The THz and far-infrared frequencies are characterized by absorption features of trace gases, in particular water vapor and oxygen.