Figure 32 - uploaded by Peter Smith
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The flux in the direct solar beam measured by the ULVS at 9 solar zenith angles as shown compared to the solar flux outside the atmosphere of the Earth.
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The payload of the Huygens Probe into the atmosphere of Titan includes the Descent Imager/Spectral Radiometer (DISR). This
instrument includes an integrated package of several optical instruments built around a silicon charge coupled device (CCD)
detector, a pair of linear InGaAs array detectors, and several individual silicon detectors. Fiber opti...
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Figure 32 shows the set of nine ULVS spectra of the direct solar beam at solar zenith angles from 25.7 ◦ to 50 ◦ . Also shown is the solar flux from Neckel and Labs (1984) convolved to the spectral resolution of the ULVS instrument. Figure 33 shows the log of the direct beam flux vs. the secant of the solar zenith angle (the airmass) at a few continuum wavelengths across the ULVS spectra of Figure 32. The natural log of the ratio of spectra at any airmass to the spectrum outside the atmosphere gives the total extinction optical depth for molecular Rayleigh scattering, aerosol particle scattering, and molecular gaseous absorption for that slant path through the atmosphere of the Earth. Figure 34 shows the total vertical extinction optical depth as a function of wavelength from the ULVS and ULIS ...
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Figure 32 shows the set of nine ULVS spectra of the direct solar beam at solar zenith angles from 25.7 ◦ to 50 ◦ . Also shown is the solar flux from Neckel and Labs (1984) convolved to the spectral resolution of the ULVS instrument. Figure 33 shows the log of the direct beam flux vs. the secant of the solar zenith angle (the airmass) at a few continuum wavelengths across the ULVS spectra of Figure 32. The natural log of the ratio of spectra at any airmass to the spectrum outside the atmosphere gives the total extinction optical depth for molecular Rayleigh scattering, aerosol particle scattering, and molecular gaseous absorption for that slant path through the atmosphere of the Earth. Figure 34 shows the total vertical extinction optical depth as a function of wavelength from the ULVS and ULIS ...
Citations
... Finally, there is the precedent of the Huygens probe for the Cassini mission, developed jointly by NASA and ESA, with the objective of studying the atmosphere of Titan. In this case, the Descent Imager/Spectral Radiometer (DISR) was the key instrument for the characterization of the aerosols (Tomasko et al. 2002). It encompassed the measurement of total solar radiation flux as well as measurements of scattering in two spectral bands and across two polarization planes, along with wavelength-dependent extinction measurements across different layers of the atmosphere. ...
The aerosols (clouds and hazes) on Uranus are one of the main elements for understanding the thermal structure and dynamics of its atmosphere. Aerosol particles absorb and scatter the solar radiation, directly affecting the energy balance that drives the atmospheric dynamics of the planet. In this sense, aerosol information such as the vertical distribution or optical properties is essential for characterizing the interactions between sunlight and aerosol particles at each altitude in the atmosphere and for understanding the energy balance of the
planet’s atmosphere. Moreover, the distribution of aerosols in the atmosphere provides key information on the global circulation of the planet (e.g., regions of upwelling or subsidence).
To address this challenge, we propose the Uranus Multi-experiment Radiometer (UMR), a lightweight instrument designed to characterize the aerosols in Uranus’ atmosphere as part of the upcoming Uranus Flagship mission’s descending probe payload. The scientific goals of UMR are: (1) to study the variation of the solar radiation in the ultra-violet (UV) with altitude and characterize the energy deposition in the atmosphere; (2) to study the vertical distribution of the hazes and clouds and characterize their scattering and optical properties; (3) to investigate the heating rates of the atmosphere by directly measuring the upward and downward fluxes; and (4) to study the cloud vertical distribution and composition at pressures where sunlight is practically negligible (p > 4-5 bars).
The instrument includes a set of photodetectors, field-of-view masks, a light infrared lamp, and interference filters. It draws on the heritage of previous instruments developed at the Instituto Nacional de Técnica Aeroespacial (INTA) that participated in the exploration of Mars, where similar technology has demonstrated its endurance in extreme environments while utilizing limited resources regarding power consumption, mass and volume footprints, and data budget. The radiometer’s design and characteristics make it a valuable complementary payload for studying Uranus’ atmosphere with a high scientific return.
... The Descent Imager/Spectral Radiometer (DISR) on the Huygens descent probe utilised a frame transfer CCD to capture images during its rapid descent, during which the probe continually rotated. The use of a large frame transfer CCD allowed several imagers to share a single detector, minimising instrument mass and complexity (Tomasko, et al., 1999). Use of the frame-transfer technique requires either a larger detector (in order to accommodate both an imaging region and storage region large enough for the desired image), or a reduction in image size. ...
... The penetrator descent camera concept observes the surface with a unique imaging geometry, distinct from any that has previously been employed (it most closely resembles the combined performance of the Huygens probe's three DISR cameras (Tomasko, et al., 1999)). Imaging characteristics, such as spatial resolution, vary significantly over the instrument's large FOV, with resolution highest at the penetrator's nadir, and decreasing monotonically as surface distance from nadir increases. ...
... 56: Illustration of an adapted implementation of EnVisS' all-sky imaging.Fisheye optics with a 180° hemispherical FOV (solid green semicircle) image through a filter wheel onto a detector to achieve hemispherical coverage of the sky. An optional second set of hemispherical-FOV optics (dashed green semicircle) imaging onto another detector (or the same detector via fibre optics, seeTomasko et al. (1999)) increases coverage to the entire visible sky.With the instrument mounted on a stabilised platform, exposure times would be limited by flyby motion, and the values possible would range from 10 ms near closest approach to as high as 100 s at the earlier stages of the flyby (from section 6.2.2.1). With these larger exposure times, which are comparable to those used by other cometary cameras such as Rosetta's OSIRIS, higher-resolution higher-SNR images could be obtained (>100 when observing a brightness of 10 -8 W m -2 sr -1 nm -1 ). ...
In this thesis, a novel approach to spaceborne imaging is investigated, building upon the scan imaging technique in which camera motion is used to construct an image. This thesis investigates its use with wide-angle (≥90° field of view) optics mounted on spin stabilised probes for large-coverage imaging of planetary environments, and focusses on two instruments. Firstly, a descent camera concept for a planetary penetrator. The imaging geometry of the instrument is analysed. Image resolution is highest at the penetrator’s nadir and lowest at the horizon, whilst any point on the surface is imaged with highest possible resolution when the camera’s altitude is equal to that point’s radius from nadir. Image simulation is used to demonstrate the camera’s images and investigate analysis techniques. A study of stereophotogrammetric measurement of surface topography using pairs of descent images is conducted. Measurement accuracies and optimum stereo geometries are presented. Secondly, the thesis investigates the EnVisS (Entire Visible Sky) instrument, under development for the Comet Interceptor mission. The camera’s imaging geometry, coverage and exposure times are calculated, and used to model the expected signal and noise in EnVisS observations. It is found that the camera’s images will suffer from low signal, and four methods for mitigating this – binning, coaddition, time-delay integration and repeat sampling – are investigated and described. Use of these methods will be essential if images of sufficient signal are to be acquired, particularly for conducting polarimetry, the performance of which is modelled using Monte Carlo simulation. Methods of simulating planetary cameras’ images are developed to facilitate the study of both cameras. These methods enable the accurate simulation of planetary surfaces and cometary atmospheres, are based on Python libraries commonly used in planetary science, and are intended to be readily modified and expanded for facilitating the study of a variety of planetary cameras.
... • Stitching of few overlapping frame images, from a small number of individual frame cameras or a single frame camera aboard a slowly rotating platform (e.g. Tomasko et al. (2002)). ...
Digital Terrain Models (DTMs) provide valuable insights into the nature of solar system surfaces, facilitating geological analysis, landing site selection and characterisation, and contextualising in situ measurements. For missions or solar system bodies for which orbiters and soft landed platforms are technologically or financially challenging to achieve, low mass descent or ascent probes (e.g. planetary penetrators) provide an alternative means by which to access the atmosphere and/or surface, and a platform from which to image the surface from a range of altitudes and perspectives. This paper presents a study into the concept of large-coverage descent stereophotogrammetry, whereby the stereo geometry of vertically offset wide-angle descent images is used to measure surface topography over a region of large extent. To do this, we simulate images of Mars’ Gale Crater using a large coverage, high resolution DTM of the area, and derive topographic measurements by stereo matching pairs of simulated images. These topographic measurements are compared directly with the original DTM to characterise their accuracy, and dependence of elevation measurement accuracy on stereo geometry is thus investigated. For a stereo pair with a given altitude (corresponding to the altitude of its lower image), error in elevation measurement is found to have its minimum value for surface at a horizontal distance between 1 and 3 times the altitude. For a point on the surface with given horizontal distance from the imaging location, a stereo imaging altitude between 0.2 and 0.5 times this distance is found to achieve best elevation measurement accuracy. Surface appearance, and its change between two images of a stereo pair, is found to have a significant impact on stereo matching performance, limiting stereo baseline length to an optimum value range of 0.2-0.4 times the lower image’s altitude, and resulting in the occurrence of occlusions and blind spots, particularly at oblique viewing angles.
... 181 The Huygens probe's payload contained six experiments: (1) the Huygens Atmospheric Structure Instrument, 182 (2) the Doppler Wind Experiment, 183 (3) the Aerosol Collector and Pyrolyzer, 184 (4) the GC-MS, 185 (5) the Surface Science Package, 186 and (6) the Descent Imager and Spectral Radiometer. 187 Measurements from the Huygens GC-MS showed the mole fraction of methane is 1.41 × 10 −2 in Titan's stratosphere and increases to 4.9 × 10 −2 near the surface, 188 which is in agreement with measurements made by the DISR. 189 Additionally, GC-MS measurements of Titan's surface confirmed the presence of ethane, while C 2 H 2 , C 2 N 2 , benzene, and CO 2 have been tentatively identified. ...
This Feature introduces and discusses the findings of key analytical techniques used to study planetary bodies in our solar system in the search for life beyond Earth, future missions planned for high-priority astrobiology targets in our solar system, and the challenges we face in performing these investigations.
... Characteristics of the DISR Downward-Looking Instruments: High-Resolution Imager (HRI), Medium-Resolution Imager (MRI), and Side-Looking Imager (SLI)(Lebreton et al., 2005;Tomasko et al., 2002Tomasko et al., , 2003 Note. The focal length is provided by Archinal et al.(2006), and the sensor size can be deduced from the size of the individual pixels/photosites found on the ESA PSA website (https://sci.esa.int/ ...
Titan, le plus gros satellite de Saturne, est un corps atypique dans le Système solaire. A commencer par sa taille planétaire, plus grande que Mercure, son atmosphère riche et dense, principalement composée de méthane et de diazote, permettant l'existence d'un cycle du méthane, similaire au cycle de l'eau sur Terre. Des vallées fluviales y ont été observées à toutes les latitudes grâce à la mission Cassini-Huygens (2004-2017). Tout comme l'eau sur Terre, le méthane liquide creuse le substrat pour former des réseaux de rivières complexes, observés dans les images acquises près de l'équateur par la sonde Huygens. Ces rivières jouent un rôle majeur dans la formation et la dynamique des paysages. L'objectif de cette thèse est de contraindre le contexte géomorphologique et climatique de mise en place de ces rivières. Cette étude est centrée sur le réseau de rivières proche du site d'atterrissage de la sonde Huygens, car il s'agit du paysage le plus résolu de la surface de Titan observé à ce jour. La réalisation d'un modèle numérique de terrain (MNT) a tout d'abord été effectuée grâce à la mise en place d'une nouvelle stratégie de reconstruction de la topographie permettant d'outrepasser la complexité du jeu de données disponible (qualité médiocre des images et géométrie d'acquisition non optimale). Ce MNT a ensuite été exploité pour analyser le paysage fluvial au travers de critères de caractérisation morphologique (indices de concavité et distribution des pentes) afin d'en extraire une signature climatique. Enfin, les taux de précipitations requis pour former ces rivières ont été calculés grâce à la théorie de la rivière au seuil. Cette étude montre que les paysages fluviaux proches du site d'atterrissage de la sonde Huygens sont soumis à un climat aride. Les rivières se forment lors d'évènements pluvieux rares et modérés (avec des taux de précipitation instantané de moins de 5 mm/h), conditions compatibles avec les observations de Cassini et les prédictions des modèles de climat actuels pour les régions équatoriales de Titan. En comparaison avec la Terre, il apparaît enfin que des débits de méthane liquide plus faibles, et donc des taux de précipitations moins élevés, sont nécessaires pour former des rivières de taille équivalente. Un certain nombre de ces résultats (notamment les taux de précipitations moyens et instantanés) pourra être vérifié par la future mission d'exploration « in situ » de Titan, Dragonfly, dont l'arrivée est prévue en 2034.
... Altimetry is required in the EDL architecture after heat shield separation, which may occur at an altitude of several 10s of km. Performance of the radar altimeter used by the Huygens probe was taken as representative for this, which had a final design goal for operation up to 60 km AGL with <5% error [30]. ...
Titan's dense atmosphere, low gravity, and high winds at high altitudes create descent times of >90 minutes with standard entry/descent/landing (EDL) architectures and result in large unguided landing ellipses, with 99% values of ⇠110x110 km and 149x72 km in recent Titan lander proposals. Enabling precision landing on Titan could increase science return for the types of missions proposed to date and make additional types of landing sites accessible, opening up new possibilities for science investigations. Precision landing on Titan has unique challenges, because the hazy atmosphere makes it difficult to see the surface and because it requires guided descent with divert ranges that are one to two orders of magnitude larger than needed for other target bodies, i.e. up to on the order of 100 km. It is conceivable that such a divert capability could be provided economically by a parafoil or other steerable aerodynamic decelerator deployed several 10s of km above the surface. The long descent times lead to large inertial navigation errors, hence a need for terrain relative navigation (TRN). This would require a TRN capability that can operate at such altitudes, despite challenges of seeing the surface sufficiently clearly and of depending on map products that are two orders of magnitude lower in spatial resolution than those for Mars and airless bodies.
This paper addressed the TRN problem for Titan guided descent , assuming parafoil deployment at an altitude around 40 km. We define a notional sensor suite including an inertial measurement unit (IMU), a radar altimeter, and two descent cameras, with spectral responses in the visible/near infrared (VNIR) (⇠0.5 to 1 um) and short wave infrared (SWIR) (⇠2.0 to 2.1 um). Due to the low resolution of current Titan map products, we define two altitude regimes (above and below ⇠20 km) that need different navigation techniques. Map matching is applicable in the upper regime, but challenging or infeasible in the lower one. Feature tracking with decent imagery is desirable in the lower regime, but challenging in the upper one. We derive image contrast requirements for TRN from prior literature and create models of achievable image contrast by radiative transfer modeling; this shows that the requirements should be achievable for a SWIR descent camera in the upper regime, and that a VNIR descent camera is preferable in the lower regime.
We then develop algorithms for map matching and feature tracking with descent images and test these with synthetic images created from Cassini/Huygens data sets and our radiative transfer model. We also introduce new possibilities for TRN based on the potential to discriminate some specific types of terrain onboard in descent imagery, such as lake vs adjacent ground and dune vs interdune. We use sensor measurement noise models in simulations of state estimation with an extended Kalman filter that includes coordinates of a set of tracked features in the state vector. Case studies were done for two notional landing sites, one in a site with only dry ground and one in a Titan lake district. In both cases, the filter error model shows 3 position error at touchdown on the order of 2 km. More work is needed to validate these results with higher fidelity camera models and larger data sets, but this is very promising.
... Jupiter's Galileo probe made its first measurements on December 7th, 1995 (Sromovsky et al. 1998). Cassini's Huygens probe included the Descent Imager/Spectral Radiometer (DISR) (Tomasko et al. 2002) and landed on Titan on January 14th, 2005. DISR only looked at upward and downward direct and diffuse solar flux between 0.35 and 1.7 µm spectral range during its descent. ...
The design of an advanced Net Flux Radiometer (NFR), for inclusion as a payload on a future Ice Giants probe mission, is given. The Ice Giants NFR (IG-NFR) will measure the upward and downward radiation flux (hence net radiation flux), in seven spectral bands, spanning the range from solar to far infra-red wavelengths, each with a \(5^{\circ}\) Field-Of-View (FOV) and in five sequential view angles (\(\pm 80^{\circ}\), \(\pm 45^{\circ}\), and \(0^{\circ}\)) as a function of altitude. IG-NFR measurements within either Uranus or Neptune’s atmospheres, using dedicated spectral filter bands will help derive radiative heating and cooling profiles, and will significantly contribute to our understanding of the planet’s atmospheric heat balance and structure, tropospheric 3-D flow, and compositions and opacities of the cloud layers. The IG-NFR uses an array of non-imaging Winston cones integrated to a matched thermopile detector Focal Plane Assembly (FPA), with individual bandpass filters, housed in a diamond windowed vacuum micro-vessel. The FPA thermopile detector signals are read out in parallel mode, amplified and processed by a multi-channel digitizer application specific integrated circuit (MCD ASIC) under field programmable gate array (FPGA) control. The vacuum micro-vessel rotates providing chopping between FOV’s of upward and downward radiation fluxes. This unique design allows for small net flux measurements in the presence of large ambient fluxes and rapidly changing ambient temperatures during the probe descent to \({\geq} 10\) bar pressure.
... Acoustic travel times can be measured to ∼10 ns for travel times in the 0.5ms range (one part in 5e-4) using a high TRL, compact, energy-efficient and low data volume ultrasonic anemometer originally developed for Mars [182]. [40], and the DISR on the Huygens Probe [184] for in situ measurements within Venus, Jupiter and Titan's atmospheres, respectively. All instruments were designed to measure the net radiative flux and upward radiation flux within their respective atmospheres as the probe descended by parachute. ...
Remote sensing observations suffer significant limitations when used to study the bulk atmospheric composition of the giant planets of our solar system. This impacts our knowledge of the formation of these planets and the physics of their atmospheres. A remarkable example of the superiority of in situ probe measurements was illustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases' abundances and the precise measurement of the helium mixing ratio were only made available through in situ measurements by the Galileo probe. Here we describe the main scientific goals to be addressed by the future in situ exploration of Saturn, Uranus, and Neptune, placing the Galileo probe exploration of Jupiter in a broader context. An atmospheric entry probe targeting the 10-bar level would yield insight into two broad themes: i) the formation history of the giant planets and that of the Solar System, and ii) the processes at play in planetary atmospheres. The probe would descend under parachute to measure composition, structure, and dynamics, with data returned to Earth using a Carrier Relay Spacecraft as a relay station. An atmospheric probe could represent a significant ESA contribution to a future NASA New Frontiers or flagship mission to be launched toward Saturn, Uranus, and/or Neptune.
... Acoustic travel times can be measured to ∼10 ns for travel times in the 0.5ms range (one part in 5e-4) using a high TRL, compact, energy-efficient and low data volume ultrasonic anemometer originally developed for Mars [182]. [40], and the DISR on the Huygens Probe [184] for in situ measurements within Venus, Jupiter and Titan's atmospheres, respectively. All instruments were designed to measure the net radiative flux and upward radiation flux within their respective atmospheres as the probe descended by parachute. ...
Remote sensing observations suffer significant limitations when used to study the bulk atmospheric composition of the giant planets of our solar system. This impacts our knowledge of the formation of these planets and the physics of their atmospheres. A remarkable example of the superiority of in situ probe measurements was illustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases' abundances and the precise measurement of the helium mixing ratio were only made available through in situ measurements by the Galileo probe. Here we describe the main scientific goals to be addressed by the future in situ exploration of Saturn, Uranus, and Neptune, placing the Galileo probe exploration of Jupiter in a broader context. An atmospheric entry probe targeting the 10-bar level would yield insight into two broad themes: i) the formation history of the giant planets and that of the Solar System, and ii) the processes at play in planetary atmospheres. The probe would descend under parachute to measure composition, structure, and dynamics, with data returned to Earth using a Carrier Relay Spacecraft as a relay station. An atmospheric probe could represent a significant ESA contribution to a future NASA New Frontiers or flagship mission to be launched toward Saturn, Uranus, and/or Neptune.
... Acoustic travel times can be measured to ∼10 ns for travel times in the 0.5ms range (one part in 5e-4) using a high TRL, compact, energy-efficient and low data volume ultrasonic anemometer originally developed for Mars [182]. [40], and the DISR on the Huygens Probe [184] for in situ measurements within Venus, Jupiter and Titan's atmospheres, respectively. All instruments were designed to measure the net radiative flux and upward radiation flux within their respective atmospheres as the probe descended by parachute. ...
Remote sensing observations suffer significant limitations when used to study the bulk atmospheric composition of the giant planets of our solar system. This impacts our knowledge of the formation of these planets and the physics of their atmospheres. A remarkable example of the superiority of in situ probe measurements was illustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases' abundances and the precise measurement of the helium mixing ratio were only made available through in situ measurements by the Galileo probe. Here we describe the main scientific goals to be addressed by the future in situ exploration of Saturn, Uranus, and Neptune, placing the Galileo probe exploration of Jupiter in a broader context. An atmospheric entry probe targeting the 10-bar level would yield insight into two broad themes: i) the formation history of the giant planets and that of the Solar System, and ii) the processes at play in planetary atmospheres. The probe would descend under parachute to measure composition, structure, and dynamics, with data returned to Earth using a Carrier Relay Spacecraft as a relay station. An atmospheric probe could represent a significant ESA contribution to a future NASA New Frontiers or flagship mission to be launched toward Saturn, Uranus, and/or Neptune.
