Browse Topic: Altimeters
This SAE Aerospace Recommended Practice (ARP) provides performance criteria for Altitude Alerting Devices and Systems. These devices can be self-contained or receive remote altitude information and can have integral or remote barometric corrections. Only the generation of the alerting signals is covered by this recommended practice and not the details of the visual or audio alerts operated by these signals. It is recommended that the system’s operational correspondence between the selected altitude settings of the Altitude Alerting Device and the Altitude Level Indication normally used to control the aircraft should not exceed ±250 ft RSS throughout the operating range of the device
Micro aerial vehicles (MAVs) are lightweight, highly dynamic vehicles with limited payload, sensing, and computation capabilities. There is significant interest to automate MAVs for military surveillance, reconnaissance, and search-and-rescue missions. The current state of the art in MAV control utilizes an external system of cameras or other sensors to localize the vehicle during flight. Precise MAV localization using onboard computing and sensing resources is required for missions in unknown indoor and outdoor environments. In general MAVs may only operate using a low-performance inertial measurement unit and a single camera, with use of other sensors such as GPS or altimeters being limited by payload or environmental constraints
The purpose of this work was to develop and demonstrate technologies for a next-generation, efficient, swath-mapping space laser altimeter. The Lidar Surface Topography (LIST) mission concept allows simultaneous measurements of 5-meter-spatial-resolution topography and vegetation vertical structure with decimeter vertical precision in an elevation imaging swath several kilometers wide from a 400-km-altitude Earth orbit. To advance and demonstrate needed technologies for the LIST mission, the Airborne LIST Simulator (ALISTS) pathfinder instrument was developed. ALISTS is a micropulse, single photon-sensitive waveform recording system based on a new and highly efficient laser measurement approach utilizing emerging laser transmitter and detector technologies
The SWOT Science Simulator simulates projected SWOT altimetry observations that can be applied to an ocean general circulation model, allowing the exploration of ideas and methods to optimize information retrieval from the proposed SWOT Mission, which is currently baselined to launch in 2020
The Twin Head Efficient Oscillator (THEO) concept uses a pair of smaller, identical laser pump modules, oriented to remove asymmetrical thermo-optical effects typical in single-slab lasers such as HOMER (High Output Maximum Efficiency Resonator), MLA (Mercury Laser Altimeter), LOLA Lunar Orbiter Laser Altimeter, and GLAS (Geoscience Laser Altimeter), while simultaneously increasing efficiency and lifetime. This creates 100+ mJ pulses in an oscillator-only design, with reduced risk of optical damage, record efficiency, high stability, long life, and high TEM00 beam quality typical of much smaller rod-based cavities. Near-field-beam quality is critical to efficient second harmonic generation (SHG 532 nm), which is typically poor in slab-based Nd:YAG lasers
This software provides storage retrieval and analysis functionality for managing satellite altimetry data. It improves the efficiency and analysis capabilities of existing database software with improved flexibility and documentation. It offers flexibility in the type of data that can be stored. There is efficient retrieval either across the spatial domain or the time domain. Built-in analysis tools are provided for frequently performed altimetry tasks
A test port designed as part of a fiber-optic-coupled laser altimeter receiver optical system allows for the back-illumination of the optical system for alignment verification, as well as illumination of the detector(s) for testing the receiver electronics and signal-processing algorithms. Measuring the optical alignment of a laser altimeter instrument is difficult after the instrument is fully assembled. The addition of a test port in the receiver aft-optics allows for the back-illumination of the receiver system such that its focal setting and boresight alignment can be easily verified. For a multiple-detector receiver system, the addition of the aft-optics test port offers the added advantage of being able to simultaneously test all the detectors with different signals that simulate the expected operational conditions
A diffractive optic element (DOE) can be used as a beam splitter to generate multiple laser beams from a single input laser beam. This technology has been recently used in LRO’s Lunar Orbiter Laser Altimeter (LOLA) instrument to generate five laser beams that measure the lunar topography from a 50-km nominal mapping orbit (see figure). An extension of this approach is to use a multiple-zone DOE to allow a laser altimeter instrument to operate over a wider range of distances. In particular, a multiple-zone DOE could be used for applications that require both mapping and landing on a planetary body. In this case, the laser altimeter operating range would need to extend from several hundred kilometers down to a few meters
A sequencer for a radar altimeter provides accurate attitude information for a reliable soft landing of the Mars Science Laboratory (MSL). This is a field-programmable-gate-array (FPGA)-only implementation. A table loaded externally into the FPGA controls timing, processing, and decision structures. Radar is memory-less and does not use previous acquisitions to assist in the current acquisition. All cycles complete in exactly 50 milliseconds, regardless of range or whether a target was found
A method of incorporating information, acquired by a multibeam laser or radar altimeter system, pertaining to the distance and direction between the system and a nearby target body, into an estimate of the state of a vehicle upon which the system is mounted, involves the use of a faceted model to represent the shape of the target body. In the original intended application, the vehicle would be a spacecraft and the target body would be an asteroid, comet, or similar body that the spacecraft was required to approach. The method could also be used in navigating aircraft at low altitudes over terrain that is rough and/or occupied by objects of significant structure
A computer program called "phxlrsim" simulates the behavior of the radar system used as an altimeter and velocimeter during the entry, descent, and landing phases of the Phoenix lander spacecraft. The simulation includes modeling of internal functions of the radar system, the spacecraft trajectory, and the terrain. The computational models incorporate representations of nonideal hardware effects in the radar system and effects of radar speckle (coherent scatter of radar signals from terrain
The terminal descent sensor (TDS) is a radar altimeter/velocimeter that improves the accuracy of velocity sensing by more than an order of magnitude when compared to existing sensors. The TDS is designed for the safe planetary landing of payloads, and may be used in helicopters and fixed-wing aircraft requiring high accuracy velocity sensing
Mercury Laser Altimeter Science Algorithms is a software system for controlling the laser altimeter aboard the Messenger spacecraft, which is to enter into orbit about Mercury in 2011. The software will control the altimeter by dynamically modifying hardware inputs for gain, threshold, channel- disable flags, range- window start location, and range- window width, by using ranging information provided by the spacecraft and noise counts from instrument hardware. In addition, because of severe bandwidth restrictions, the software also selects returns for downlink. To reduce mission risk, the software incorporates three different modes of operation. The three modes are denoted as fixed, range-driven, and closed-loop (or adaptive). The fixed mode provides fixed hardware inputs for all but the threshold. The range-driven mode receives and utilizes ranging information from the spacecraft regarding its slant range to the planet or asteroid. The adaptive mode is capable of improving upon the
would be capable of real-time, onboard processing of complete sets of interferometric radar data is undergoing development. Intended for original use as part of a spaceborne interferometric radar system, this data-processing system or parts of it could be adapted to diverse other remote-sensing systems, including spaceborne and airborne synthetic- aperture radar systems, radar altimeters, and collision-avoidance radar systems
A computer program has been written to perform several analyses of radar altimeter data. The program was designed to improve on previous methods of analysis of altimeter engineering data by (1) facilitating and accelerating the analysis of large amounts of data in a more direct manner and (2) improving the ability to estimate performance of radar-altimeter instrumentation and provide data corrections. The data in question are openly available to the international scientific community and can be downloaded from anonymous file-transfer-protocol (FTP) locations that are accessible via links from altimetry Web sites. The software estimates noise in range measurements, estimates corrections for electromagnetic bias, and performs statistical analyses on various parameters for comparison of different altimeters. Whereas prior techniques used to perform similar analyses of altimeter range noise require comparison of data from repetitions of satellite ground tracks, the present software uses a
CryoSat is the first satellite of ESA's Living Planet Programme realised in the framework of the Earth Explorer Opportunity Missions. CryoSat is a radar altimeter mission dedicated to determine trends in the ice masses of the Earth. The overall spacecraft configuration was driven by the budget constraints applicable for the opportunity mission, the high inclination orbit with drifting orbit plane and the stringent stability requirements for the radar altimeter antennas. Innovative thermal design solutions were needed for the following items: The instrument antennas have to comply with very stringent pointing stability requirements. The star trackers need to be mounted at a thermally adverse position and still have to be maintained on low temperature levels. The instrument electronics must be close to the antennas leaving no possibility for direct rejection of heat by radiation The battery has contrary temperature requests from lifetime respectively performance point of view and needs
A lidar apparatus called a microaltimeter has been proposed for use aboard a spacecraft in orbit around the Earth for mapping land and sea surfaces, including such features of special interest as ice, tree canopies, and flood plains. The microaltimeter is short for "microlaser altimeter" and is so named because it uses a very compact, low-energy, subnanosecond pulse, solid-state microlaser as its source and relatively small (typically 10 to 20 cm in diameter) telescopes, resulting in a factor of 100 reduction in telescope weight and volume, as compared to conventional spaceborne laser altimeters. Operating at thousands of pulses per second, the surface sampling rate is approximately 100 times higher than that of prior spaceborne laser altimeters having the same transmitter power-aperture product
Radar Altimeters are being included in several existing Air Force aircraft. Of these, the A-10, F-15, and the F-16 are also envisioned to perform the night, under the weather attack mission. This mission, coupled with limited available cockpit space and the anticipated high pilot workload has led to a design effort to include the radar altimeter on the HUD. The LANTIRN system offered a key opportunity to accomplish this HUD integration. The design has evolved from pilot opinions through simulation and now flight test. Plans are currently being made to conduct a simulation to make minor changes to the display based on test results to further optimize the display. This radar altimeter design and particularly the way the design has evolved should serve as examples for future efforts. Of particular note is that this display has been designed from the beginning for a specific purpose and is being optimized for its intended operational environment and the pilots who will use it
An analytical study using computer thermal models to investigate the feasibility of replacing the MRA (Missile Radar Altimeter) aluminum case with TORLON 5030, a polyamide-imide thermoplastic (1)*, is presented. The MRA case was selected because the MRA is used for several different missiles, and the resultant higher quantities provides a cost saving potential. The feasibility of using TORLON cases in electronic equipment is determined by heat generation rates, methods of cooling and the severity of the thermal environment. Since TORLON has considerably lower thermal conductivity compared to aluminum, knowing the critical thermal paths in the electronic equipment case is essential in arriving at an optimum design/combination of TORLON and aluminum. Five different designs using TORLON were analyzed by computing component temperatures and comparing them with those of an all-aluminum baseline design. The five design concepts are: 1. An all-TORLON (sidewalls and baseplate) case; 2. TORLON
This Aeronautical Standard covers two basic types of instruments as follows: Type I - Range 35,000 feet. Barometric Pressure. Scale range at least 28.1 - 30.99 inches of mercury (946 - 1049 millibars). May include markers working in conjunction with the Barometric Pressure Scale to indicate pressure-altitude. Type II - Range 50,000 feet. Barometric Pressure. Scale range at least 28.1 - 30.99 inches of mercury (946 - 1049 millibars). May include markers working in conjunction with the Barometric Pressure Scale to indicate pressure-altitude
This Aeronautical Standard covers two basic types of instruments as follows
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