Information Technology & Software

Efficient Method for Optimizing Placement of Sensors

This systematic method supplants ad hoc placement and exhaustive-search optimization methods.

A computationally efficient method has been developed to enable optimization of the placement of sensors for the purpose of diagnosis of a complex engineering system (e.g., an aircraft or spacecraft). The method can be used both in (1) designing a sensor system in which the number and positions of sensors are initially not known and must be determined and (2) adding sensors to a pre-existing system to increase the diagnostic capability.

Posted in: Briefs, TSP, Information Sciences, Optimization, Sensors and actuators

Truncation Depth Rule-of-Thumb for Convolutional Codes

The new rule is more accurate and tight at high signal-to-noise ratios.

In this innovation, it is shown that a commonly used rule of thumb (that the truncation depth of a convolutional code should be five times the memory length, m, of the code) is accurate only for rate 1/2 codes. In fact, the truncation depth should be 2.5 m/(1 – r), where r is the code rate. The accuracy of this new rule is demonstrated by tabulating the distance properties of a large set of known codes. This new rule was derived by bounding the losses due to truncation as a function of the code rate.

Posted in: Briefs, TSP, Information Sciences, Mathematical models, Product development

Multibeam Altimeter Navigation Update Using Faceted Shape Model

The model is applicable to a body having almost any complex shape.

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.

Posted in: Briefs, Information Sciences, Mathematical models, Altimeters, Flight guidance systems, Lasers, Radar

MODIS Atmospheric Data Handler

A number of science data sets are derived from the observations of the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard NASA’s Terra and Aqua satellites. These data typically contain information on retrieval techniques, quality-control flags, and geo-referencing information. These datasets, distributed in HDF (Hierachical Data Format), must be further processed to extract relevant information for weather analysis studies and numerical models input. The MODIS-Atmosphere Data Handler software converts the HDF data to ASCII format, and outputs: (1) atmospheric profiles of temperature and dew point and (2) total precipitable water. Quality-control data are also considered in the export procedure.

Posted in: Briefs, Information Sciences, Imaging and visualization, Data management, Quality control, Satellites

Reducing Surface Clutter in Cloud Profiling Radar Data

Radar data can be processed to study clouds closer to the surface.

An algorithm has been devised to reduce ground clutter in the data products of the CloudSat Cloud Profiling Radar (CPR), which is a nadir-looking radar instrument, in orbit around the Earth, that measures power backscattered by clouds as a function of distance from the instrument. Ground clutter contaminates the CPR data in the lowest 1 km of the atmospheric profile, heretofore making it impossible to use CPR data to satisfy the scientific interest in studying clouds and light rainfall at low altitude.

Posted in: Briefs, Information Sciences, Mathematical models, Radar, Test equipment and instrumentation

Specialized Color Function for Display of Signed Data

This Mathematica script defines a color function to be used with Mathematica’s plotting modules for differentiating data attaining both positive and negative values. Positive values are shown as shades of blue, and negative values are shown in red. The intensity of the color reflects the absolute value of the data value.

Posted in: Briefs, Information Sciences, Mathematical models, Displays, Identification

Spatial and Temporal Low-Dimensional Models for Fluid Flow

A document discusses work that obtains a low-dimensional model that captures both temporal and spatial flow by constructing spatial and temporal four-mode models for two classic flow problems. The models are based on the proper orthogonal decomposition at two reference Reynolds numbers. Model predictions are made at an intermediate Reynolds number and compared with direct numerical simulation results at the new Reynolds number.

Posted in: Briefs, TSP, Information Sciences, Simulation and modeling

Converting From DDOR SASF to APF

A computer program called “ddor_sasf2apf” converts delta-door (delta differential one-way range) request from an SASF (spacecraft activity sequence file) format to an APF (apgen plan file) format for use in the Mars Reconnaissance Orbiter (MRO) mission-planning-and- sequencing process. The APF is used as an input to “APGEN/AUTOGEN” in the MRO activity- planning and command-sequence-generating process to sequence the delta-door (DDOR) activity. The DDOR activity is a spacecraft tracking technique for determining spacecraft location.

Posted in: Briefs, Information Sciences, Communication protocols, Computer software and hardware, Surveillance, Spacecraft

Converting From CVF to AAF

A computer program called “dsn config converter” automates what had been a manual process for updating the multi-mission adaptation file (multi.aaf) used by a multiple- mission- command- sequence- generating process comprised of a combination of the AUTOGEN and APGEN programs mentioned in the immediately preceding article. The program converts the dsn_config.cvf file that provides DSN (Deep Space Network) antenna configuration code mappings from a context variable file (CVF) format used in another part of the command generation process to an APGEN activity file (AAF) format used by AUTOGEN and APGEN.

Posted in: Briefs, Information Sciences, Communication protocols, Computer software and hardware, Flight management systems, Automation

Documenting AUTOGEN and APGEN Model Files

A computer program called “autogen hypertext map generator” satisfies a need for documenting and assisting in visualization of, and navigation through, model files used in the AUTOGEN and APGEN software mentioned in the two immediately preceding articles. This program parses autogen script files, autogen model files, PERL scripts, and apgen activity-definition files and produces a hypertext map of the files to aid in the navigation of the model. This program also provides a facility for adding notes and descriptions, beyond what is in the source model represented by the hypertext map. Further, this program provides access to a summary of the model through variable, function, sub routine, activity and resource declarations as well as providing full access to the source model and source code. The use of the tool enables easy access to the declarations and the ability to traverse routines and calls while analyzing the model.

Posted in: Briefs, Information Sciences, Cartography, Computer software and hardware, Human machine interface (HMI)

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