Ontario Lacus is a lake composed of methane , ethane and propane near the south pole of Saturn 's moon Titan . Its character as a hydrocarbon lake was confirmed by observations from the Cassini spacecraft, published in the 31 July 2008 edition of Nature . Ontario Lacus has a surface area of about 15,000 square kilometers (5,800 sq mi), about 20% smaller than its terrestrial namesake, Lake Ontario in North America . In April 2012, it was announced that it may be more like a mudflat or salt pan .
32-510: On January 12, 2010, Cassini took a more detailed radar-image of Ontario Lacus showing numerous remarkable features. The northern shoreline features low hills , probably about 1 kilometer (3,000 feet) high, and flooded river valleys . A smooth wave-sculpted shoreline, like on the southeast side of Lake Michigan , can be seen at the northeast part of the lake. Smooth lines parallel to the current shoreline could be formed by low waves over time, which were likely driven by winds sweeping in from
64-426: A flight path and the area illuminated by the radar, or footprint, is moved along the surface in a swath, building the image as it does so. Digital radar images are composed of many dots. Each pixel in the radar image represents the radar backscatter for that area on the ground ( terrain return ): brighter areas represent high backscatter, darker areas represents low backscatter. The traditional application of radar
96-414: A sharp beam. The sharpness of the beam defines the azimuth resolution. An airborne radar could collect data while flying this distance and process the data as if it came from a physically long antenna. The distance the aircraft flies in synthesizing the antenna is known as the synthetic aperture. A narrow synthetic beam width results from the relatively long synthetic aperture, which gets finer resolution than
128-420: A smaller physical antenna. Inverse synthetic aperture radar (ISAR) is another kind of SAR system which can produce high-resolution on two- and three-dimensional images. An ISAR system consists of a stationary radar antenna and a target scene that is undergoing some motion. ISAR is theoretically equivalent to SAR in that high-azimuth resolution is achieved via relative motion between the sensor and object, yet
160-416: A target with a laser and analyzing the reflected light. Laser radar is used for multi-dimensional imaging and information gathering. In all information gathering modes, lasers that transmit in the eye-safe region are required as well as sensitive receivers at these wavelengths. 3-D imaging requires the capacity to measure the range to the first scatter within every pixel. Hence, an array of range counters
192-430: A wave in the first place, comparable of building a sand castle with bone dry sand. Alternatively, the lack of waves could indicate either wind speeds less than 0.5 m/s, or an unexpectedly viscous composition of the hydrocarbon-mix fluid. In any case, the apparent presence of a wave-generated beach on the lake's northeast shore suggests that at times considerably higher waves form. Imaging radar Imaging radar
224-419: Is a form of radar that transmits a narrow angle beam of pulse radio wave in the range direction at right angles to the flight direction and receives the backscattering from the targets which will be transformed to a radar image from the received signals. Usually the reflected pulse will be arranged in the order of return time from the targets, which corresponds to the range direction scanning. The resolution in
256-413: Is a form of radar which moves a real aperture or antenna through a series of positions along the objects to provide distinctive long-term coherent-signal variations. This can be used to obtain higher resolution. SARs produce a two-dimensional (2-D) image. One dimension in the image is called range and is a measure of the "line-of-sight" distance from the radar to the object. Range is determined by measuring
288-402: Is an application of radar which is used to create two-dimensional images , typically of landscapes. Imaging radar provides its light to illuminate an area on the ground and take a picture at radio wavelengths. It uses an antenna and digital computer storage to record its images. In a radar image, one can see only the energy that was reflected back towards the radar antenna. The radar moves along
320-502: Is needed. A monolithic approach to an array of range counters is being developed. This technology must be coupled with highly sensitive detectors of eye-safe wavelengths. To measure Doppler information requires a different type of detection scheme than is used for spatial imaging. The returned laser energy must be mixed with a local oscillator in a heterodyne system to allow extraction of the Doppler shift. Synthetic-aperture radar (SAR)
352-402: Is often adequate to discriminate between various missiles, military aircraft, and civilian aircraft. Rolling is side to side. Pitching is forward and backwards, yawing is turning left or right. Monopulse radar 3-D imaging technique uses 1-D range image and monopulse angle measurement to get the real coordinates of each scatterer. Using this technique, the image doesn't vary with the change of
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#1732876045182384-451: Is then mapped onto a two-dimensional plane, with points with a higher reflectivity getting assigned usually a brighter color, thus creating an image. Several techniques have evolved to do this. Generally they take advantage of the Doppler effect caused by the rotation or other motion of the object and by the changing view of the object brought about by the relative motion between the object and
416-452: Is to display the position and motion of typically highly reflective objects (such as aircraft or ships ) by sending out a radiowave signal, and then detecting the direction and delay of the reflected signal. Imaging radar on the other hand attempts to form an image of one object (e.g. a landscape) by furthermore registering the intensity of the reflected signal to determine the amount of scattering . The registered electromagnetic scattering
448-403: Is valued for combining all the benefits of camera, LIDAR, thermal imaging and ultrasonic technologies, with additional benefits: Terrain return The terrain return is the signal returned from the ground surface when sensed by various remote sensing systems, e.g., radars . One may distinguish two components of terrain return: the wanted signal (e.g., when generating a radar map of
480-537: The ISAR moving target scene is usually made up of non cooperative objects. Algorithms with more complex schemes for motion error correction are needed for ISAR imaging than those needed in SAR. ISAR technology uses the movement of the target rather than the emitter to make the synthetic aperture. ISAR radars are commonly used on vessels or aircraft and can provide a radar image of sufficient quality for target recognition. The ISAR image
512-616: The back-scatter that is perceived by the radar of the object (typically, a plane) flying over the earth. Through recent improvements of the techniques, radar imaging is getting more accurate. Imaging radar has been used to map the Earth, other planets, asteroids, other celestial objects and to categorize targets for military systems. An imaging radar is a kind of radar equipment which can be used for imaging. A typical radar technology includes emitting radio waves, receiving their reflection, and using this information to generate data. For an imaging radar,
544-446: The image obtained by monopulse radar 3-D imaging is the physical image which is consistent with the real size of the object. 4D imaging radar leverages a Multiple Input Multiple Output (MiMo) antenna array for high-resolution detection, mapping and tracking of multiple static and dynamic targets simultaneously. It combines 3D imaging with Doppler analysis to create the additional dimension – velocity. A 4D imaging radar system measures
576-474: The lake, suggesting seasonal rainfall may be responsible for filling liquids in the local depression. This situation may be analogous to the ephemeral filling of Lake Eyre in Australia due to its notably large catchment area and the semi-arid climate of central Australia. Any waves on the lake are also far smaller than those that would be on a sizable body of liquid water on Earth; their estimated maximum height
608-457: The range direction depends on the pulse width. The resolution in the azimuth direction is identical to the multiplication of beam width and the distance to a target. The AVTIS radar is a 94 GHz real aperture 3D imaging radar. It uses Frequency-Modulated Continuous-Wave modulation and employs a mechanically scanned monostatic with sub-metre range resolution. Laser radar is a remote sensing technology that measures distance by illuminating
640-437: The returning waves are used to create an image. When the radio waves reflect off objects, this will make some changes in the radio waves and can provide data about the objects, including how far the waves traveled and what kind of objects they encountered. Using the acquired data, a computer can create a 3-D or 2-D image of the target. Imaging radar has several advantages. It can operate in the presence of obstacles that obscure
672-572: The south end of Lake Albert between Uganda and the Democratic Republic of Congo in Africa and in the remains of an ancient lake known as Megachad in the African country Chad . Infrared observations show that the southwest shoreline of the lake receded 9–11 km over four years (2005-2009), evidently due to evaporation during the dry southern hemisphere autumn. Over the same interval, no change
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#1732876045182704-551: The target's movement. Monopulse radar 3-D imaging utilizes the ISAR techniques to separate scatterers in the Doppler domain and perform monopulse angle measurement. Monopulse radar 3-D imaging can obtain the 3 views of 3-D objects by using any two of the three parameters obtained from the azimuth difference beam, elevation difference beam and range measurement, which means the views of front, top and side can be azimuth-elevation, azimuth-range and elevation-range, respectively. Monopulse imaging generally adapts to near-range targets, and
736-478: The target, and can penetrate ground (sand), water, or walls. Applications include: surface topography & coastal change; land use monitoring, agricultural monitoring, ice patrol, environmental monitoring ;weather radar- storm monitoring, wind shear warning;medical microwave tomography; through wall radar imaging; 3-D measurements, etc. Wall parameter estimation uses Ultra Wide-Band radar systems. The handle M-sequence UWB radar with horn and circular antennas
768-417: The terrain (large isolated scatterers and area scatter). The image record of the radar terrain return depends on the frequency, angle of incidence, and polarization of the signal. This dependence varies with the nature of the terrain surface; for example, if the terrain is covered by vegetation, a 35GHz K band signal will record vegetation, while a 0.4GHz P band signal will penetrate vegetation and record
800-419: The terrain or when used for terrain avoidance and collision detection ) and ground clutter , an unwanted signal that interferes with sensing of various objects other than terrain. The ground-to-air terrain return at vertical or near-vertical incidence angles may be decomposed into two components: a mirror-like specular component and the scatter component produced by reradiation from the individual scatterers in
832-437: The time from transmission of a pulse to receiving the echo from a target. Also, range resolution is determined by the transmitted pulse width. The other dimension is called azimuth and is perpendicular to range. The ability of SAR to produce relatively fine azimuth resolution makes it different from other radars. To obtain fine azimuth resolution, a physically large antenna is needed to focus the transmitted and received energy into
864-451: The time of flight from each transmitting (Tx) antenna to a target and back to each receiving (Rx) antenna, processing data from the numerous ellipsoids formed. The point at which the ellipsoids intersect – known as a hot spot - reveals the exact position of a target at any given moment. Its versatility and reliability make 4D imaging radar ideal for smart home, automotive, retail, security, healthcare and many other environments. The technology
896-587: The volume of Earth's Lake Ontario. The notoriously shallow Lake Okeechobee in Florida has a similar depth. Ontario Lacus may resemble a semi-arid shallow depression lying in an alluvial fan where the water table height (of liquid hydrocarbons) rises above the elevation of the depression floor, analogous to the Etosha Pan in Namibia. Hydrological runoff models have found evidence for an extensive basin catchment area for
928-445: The west or southwest. The southeast shore features a round-headed bay intruding into the shore. The middle part of the western shoreline shows the first well-developed river delta observed on Titan, showing that liquid hydrocarbons flowing down from a higher plain have switched channels on their way into the lake, forming at least two lobes. Examples of this kind of channel switching and wave-modified deltas can be found on Earth at
960-463: Was less than 3 mm during observations of a radar specular reflection during Cassini' s T49 flyover of July 2009. On Titan, waves can be generated at lower wind speeds than on Earth, due to the four times greater atmospheric density, and should be seven times higher at a given wind speed, due to Titan's surface gravity being one seventh as strong. On the other hand, pure liquid methane is only half as dense as water and may not be dense enough to form
992-507: Was observed in the south or southeast shorelines, indicating steeper slopes there. The sizes of northern hemisphere lakes and maria, in contrast, have been much more stable. By terrestrial standards, the lake appears to be extremely shallow. Radar measurements made in July 2009 and January 2010 indicate an average depth of 0.4 – 3.2 m, and a maximum depth of 2.9 – 7.4 m. This gives the lake an estimated volume of 7 to 50 km, less than one thirtieth
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1024-507: Was used for data gathering and supporting the scanning method. 3-D measurements are supplied by amplitude-modulated laser radars—Erim sensor and Perceptron sensor. In terms of speed and reliability for median-range operations, 3-D measurements have superior performance. Current radar imaging techniques rely mainly on synthetic aperture radar (SAR) and inverse synthetic aperture radar (ISAR) imaging. Emerging technology utilizes monopulse radar 3-D imaging. Real aperture radar ( RAR )
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