Abstract Reliable and accurate environmental sensing is a cornerstone of modern meteorology. This paper presents a laboratory environmental simulator capable of reproducing extreme environments and performing tests and calibrations of meteorological sensor systems under controlled conditions. This facility is available to the research community as well as industry and is intended to encourage advancement in the field of sensor metrology applied to meteorology and climatology. Discussion will be made of the temperature, pressure, humidity and wind flow control, and sensing systems with reference to specific sensor test programs and future research activities.
The Ganymede Laser Altimeter (GALA) on board the Jupiter Icy Moons Explorer (JUICE) is currently on its way to its targets, the Galilean Moons. Following the launch of the mission in April 14th 2023 the instruments on board have been checked for functionality and performance. While these regular checkouts were performed in cruise, the upcoming flyby at Earth’s Moon will give a unique opportunity to receive ground returns, assess ranging performance, and calibrate the instrument.GALA is an active instrument emitting short laser pulses (about 5 ns) of infrared radiation (at 1064 nm) to its target. Nominally, GALA emits 30 shots per second with a pulse energy of 17 mJ and a pulse divergence of 100 µrad (full cone). The receiver collects a small fraction of the reflected laser light and the round-trip travel time of the pulse is measured by the instrument electronics. In contrast to previous planetary laser altimeters, GALA features a high-frequency (200 MHz) temporal sampling of the return pulse. This enhances significantly the precision of range measurements and allows a reliable estimate of the surface roughness and albedo at the footprint scale. Performance estimates based on dark-noise measurements in cruise checkouts and models of surface properties suggest a maximal ranging distance of 1400 km for Ganymede, 1600 km for Europa, and 1100 km for Callisto. At these distances the signal-to-noise ratio for a large fraction of possible return pulse widths is larger than 1, which comprises the detection limit for GALA (see Figure 1).Current performance estimates of GALA will come to a powerful test at the lunar flyby, where measurement conditions are challenging: (1) the range to the lunar surface is above 800 km; (2) observation geometries are at an oblique angle due to the fixed inertial pointing of JUICE and (3) the albedo of the lunar surface, in particular the mare areas, is lower than on the icy satellites. Despite these challenges, current modelling suggests that GALA will be able to obtain a topographic profile of the lunar surface, which will be used to calibrate, in particular, GALA’s albedo measurement and the orientation of the transmitter boresight vector. The latter will be also determined by a cross-calibration to the JANUS camera on JUICE using data from the night side. For that purpose, JANUS will take long-exposure images during GALA operation. With that procedure it is expected to precisely locate GALA’s footprint in the detector of JANUS and thus to precisely constrain the relative orientation of the boresight vectors of the two instruments.Figure 1: Signal-to-noise ratio (SNR) for GALA at Europa (top), Ganymede (middle) and Callisto (bottom). The black dashed line shows SNR values of 10 and the dashed white line an SNR of 1.
To date dynamical observations of the Venus clouds have delivered mainly either only short‐term or long‐term averaged results. With the Venus Monitoring Camera (VMC) it finally became possible to investigate the global dynamics with a relatively high resolution in space and time on a long‐term basis. Our findings from manual cloud feature wind tracking in VMC UV image sequences so far show that the details of the mesospheric dynamics of Venus appear to be highly variable. Although the general rotation of the atmosphere remained relatively stable since Mariner 10, more than 30 years ago, by now, there are indications of short‐term variations in the general circulation pattern of the Venus atmosphere at cloud top level. In some cases, significant variations in the zonal wind properties occur on a timescale of days. In other cases, we see rather stable conditions over one atmospheric revolution, or longer, at cloud top level. It remains an interesting question whether the irregularly observed midlatitude jets are indeed variable or simply become shielded from view by higher H 2 SO 4 haze layers for varying time intervals. Winds at latitudes higher than 60°S are still difficult to obtain track because of low contrast and scarcity of features but increasing data is being collected. Over all, it was possible to extend latitudinal coverage of the cloud top winds with VMC observations. Thermal tides seem to be present in the data, but final confirmation still depends on synthesis of Visible and Infrared Thermal Imaging Spectrometer and VMC observations on night and dayside. Although poorly resolved, meridional wind speed measurements agree mainly with previous observations and with the presence of a Hadley cell spanning between equatorial region and about 45°S latitude.
[1] We use data from the High Resolution Imaging Science Experiment (HiRISE) camera and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) imaging spectrometer onboard the Mars Reconnaissance Orbiter to follow the evolution of the appearance and composition of 12 regions of the south polar layered deposits from spring to summer time. We distinguish three steps in the evolution of the volatile layer: a decrease of both CO2 band strength and albedo until Ls = 190°–210°, a significant increase in both until Ls = 240°–260° and finally a rapid decrease until the complete defrosting of the ground. In contrast, the water ice band displays a more monotonic decrease. Analysis of HiRISE color images acquired simultaneously with CRISM data allows a plausible interpretation of this evolution. In early springtime (Ls < 200°), intense jet activity results in deposition of fans of large mineral grains and a wide spatial distribution of fine grains. The small-scale topography controls the presence and location of the jets by allowing more solar energy to be collected on slopes. Grains from the dust fans warm and sink through the CO2 layer, resulting in a bluish color at the locations of the fans around Ls = 190°–210°. As the atmosphere warms up, the surface of the ice layer sublimes and releases dust and water, resulting in its brightening. The last phase of the process consists in a progressive defrosting resulting in a patchwork of frozen and unfrozen areas.
Observations acquired at ultraviolet wavelengths are uniquely well-suited to investigate the composition and structure of Enceladus' plume. This paper describes the observations, analysis techniques and results of all the Enceladus occultations observed by Cassini's Ultraviolet Imaging Spectrograph (UVIS) and other observations designed to study the plume. Limits on gas at non-polar latitudes are derived. Constraints on the minor constituents' composition of Enceladus' primarily water vapor plume are evaluated. The overall source rate variability over a time span of 13 years is < 15%, although gas output in collimated supersonic jets may vary diurnally. The average source rate for water molecules is 300 kg/s. Local enhancement of gas in the plume due to supersonic gas jets is still detectable at heights over 100 km.
