5:15 PM - 6:45 PM
[PCG21-P09] Investigation of the frequency bands for observing high-altitude water vapor on Mars by Terahertz Heterodyne Spectrometer
Keywords:Martian Atmosphere, Terahertz Spectroscopy, Water Vapor, Limb Sounding
We are designing a Terahertz Heterodyne Spectrometer Sensor(THSS) with the prospect of incorporating it into future Mars exploration missions as a sub-payload of Mars Ice Mapper(MIM) project. THSS operates at long wavelengths, which are not easily absorbed or scattered by dust and do not require a background light source like the sun, allowing observation regardless of day or night. The THSS is designed to observe three bands: In Band 1 at 400 GHz, it will capture atmospheric dynamics such as wind fields and atmospheric gravity waves by observing the CO spectrum to improve weather forecasting GCM models for manned missions and enhance the landing accuracy of spacecraft. In Band 2 at 800 GHz, it will grasp diurnal and seasonal variations of trace molecules such as low-altitude isotopes of H2O and CO, Ox, and HOx, to elucidate the atmospheric material circulation and the chemical reaction network. In Band 3, to capture water vapor to investigate how the water is transported to the upper atmosphere, we considered assigning the optically thick H2O spectrum at 560 GHz band and studied the frequency setting based on radiative transport models.
THSS uses the Double Side Band observation technique, allowing for the simultaneous detection of H2O and H217O by utilizing the overlap of the Upper Side Band and Lower Side Band. The observed signals are separeted by a frequency separation filter between Band1/Band 3 and Band 2. A digital Fourier Transform Spectrometer is assumed to be used for the spectrometer. Since the power consumption of the satellite is limited, the IF bandwidth is set to 4 GHz or lower and the frequency resolution to 1 MHz for Band 3 in this simulation, in order to minimize the power consumption. The observation method is Limb Sounding, and the atmospheric model is based on the Mars Climate Database of Mars perihelion at Ls=270°. As a result, we were able to select a band including H2O ad H217O lines and the altitude distribution of water molecules could be observed seamlessly from low to high altitudes, as well as capturing water vapor above altitudes of 100 km. We also confirmed that 18OCO and 13CO can be observed simultaneously depending on the local oscillator signal settings. In this presentation, we will report the brief results of these studies.
THSS uses the Double Side Band observation technique, allowing for the simultaneous detection of H2O and H217O by utilizing the overlap of the Upper Side Band and Lower Side Band. The observed signals are separeted by a frequency separation filter between Band1/Band 3 and Band 2. A digital Fourier Transform Spectrometer is assumed to be used for the spectrometer. Since the power consumption of the satellite is limited, the IF bandwidth is set to 4 GHz or lower and the frequency resolution to 1 MHz for Band 3 in this simulation, in order to minimize the power consumption. The observation method is Limb Sounding, and the atmospheric model is based on the Mars Climate Database of Mars perihelion at Ls=270°. As a result, we were able to select a band including H2O ad H217O lines and the altitude distribution of water molecules could be observed seamlessly from low to high altitudes, as well as capturing water vapor above altitudes of 100 km. We also confirmed that 18OCO and 13CO can be observed simultaneously depending on the local oscillator signal settings. In this presentation, we will report the brief results of these studies.