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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Users guide for an Airborne Windshear Doppler Radar Simulation (AWDRS) program

A description is provided of the Airborne Windshear Doppler Radar Simulation (AWDRS) program developed for NASA-Langley by the Research Triangle Institute. The radar simulation program is a comprehensive calculation of the signal characteristics and expected outputs of an airborne coherent pulsed Doppler radar system viewing a low level microburst along or near the approach path of the aircraft. The detailed nature of the simulation permits the quick evaluation of proposed trade-offs in radar system parameters and the evaluation of the performance of proposed configurations in various microburst/clutter environments. The simulation also provides a test bed for various proposed signal processing techniques for minimizing the effects of noise, phase jitter, and ground clutter and maximizing the useful information derived for avoidance of microburst windshear by aircraft.

Britt, Charles L.↗
NASA NTRSDate not supplied

CRTM Microwave Cloud Scattering Lookup Tables and Radar Simulator

Microwave observations play a very important role in improving the weather forecasts. Although these observations are routinely assimilated into NWP models in clear-sky conditions, assimilation of all-sky microwave observations is very limited. Two main factors contributing to this limitation are inaccuracy in the input cloud and hydrometeor profiles used as input to the radiative transfer model and also error in scattering calculations performed by the radiative transfer model itself. The Mie theory is used by many fast RT models to estimate the optical properties of single particles. The Mie theory assumes spherical shapes for ice or snow particles with mixture of air and ice. However, hydrometeors scattering radiation at microwave frequencies have different shapes, sizes, and orientations. Therefore, using Mie theory to determine their optical properties leads to large uncertainties in all-sky radiative transfer calculations. The discrete dipole approximation (DDA) which approximates the optical properties of large objects in terms of discrete dipoles has shown promise in calculating the scattering properties of particles with different shapes in the microwave frequencies. This presentation focuses on recent advancements in the CRTM scattering calculations for frozen hydrometeors in the microwave frequencies using the DDA technique. In addition to using stand-alone CRTM calculations using collocated ATMS and reanalysis profiles, the data assimilation experiments conducted using the NOAA FV3GFS forecast system are used to evaluate the scattering improvements. Additionally, the backscattering information from the DDA database was used to implement a radar simulator into CRTM. The radar operator takes advantage of CRTM different modules to calculate clouds absorption and scattering properties. In addition to the forward model both adjoint and tangent linear of the radar simulator are implemented and evaluated as well. The radar simulator is currently being tested within the JEDI/GEOS data assimilation framework to facilitate the assimilation of radar measurements such as CloudSat CPR and GPM DPR into the NASA GEOS model.

Isaac Moradi↗
NASA NTRS1986

Distributed synthetic aperture radar simulation

Synthetic aperture radar (SAR) depends primarily on attainable frequency resolution rather than on large physical size of the antenna array. The distributed architecture concept (DSAR) incorporates active elements (amplifiers) at or near the elemental radiators of the array. Since SAR's are expensive to build and expensive to test, a computer modeling approach is a feasible method of predicting the quality or nature of the SAR image from the proposed system parameters. The goal of this project is to produce a DSAR simulation software package. This report describes the progress made thus far and the work which remains to be done. Extensive work on this project had been done previously by two NASA contractors. The principal task remaining involved the creation of a suitable interface between these programs and the hardware and software available at the Johnson Space Center.

Bourgeois, B. A.↗
NASA NTRS1991

Radar simulation program upgrade and algorithm development

The NASA Radar Simulation Program is a comprehensive calculation of the expected output of an airborne coherent pulse Doppler radar system viewing a low level microburst along or near the approach path. Inputs to the program include the radar system parameters and data files that contain the characteristics of the microbursts to be simulated, the ground clutter map, and the discrete target data base which provides a simulation of the moving ground clutter. For each range bin, the simulation calculates the received signal amplitude level by integrating the product of the antenna gain pattern and the scattering source amplitude and phase of a spherical shell volume segment defined by the pulse width, radar range, and ground plane intersection. A series of in-phase and quadrature pulses are generated and stored for further processing if desired. In addition, various signal processing techniques are used to derive the simulated velocity and hazard measurements, and store them for use in plotting and display programs.

Britt, Charles L.↗
NASA NTRS1988

Wind shear radar simulation

Viewgraphs used in a presentation on wind shear radar simulation are given. Information on a microburst model of radar reflectivity and wind velocity, radar pulse output, the calculation of radar return, microburst power spectrum, and simulation plans are given. A question and answer session is transcribed.

Britt, Charles L.↗
NASA NTRS1991

3-D laser radar simulation for autonomous spacecraft landing

A sophisticated 3D laser radar sensor simulation, developed and applied to the task of autonomous hazard detection and avoidance, is presented. This simulation includes a backward ray trace to sensor subpixels, incoherent subpixel integration, range dependent noise, sensor point spread function effects, digitization noise, and AM-CW modulation. Specific sensor parameters, spacecraft lander trajectory, and terrain type have been selected to generate simulated sensor data.

Reiley, Michael F.↗
NASA NTRS1992

Infrared, microwave, and spaceborne radar simulations of a deep convective system using a 3-D cloud ensemble method

A 3D cloud model is used to simulate the storm structure, and the results are linked to microwave and infrared radiative transfer models for simulation of aircraft observations. Spaceborne radar data are also simulated along the aircraft flight track. The cloud and radiative model simulations are studied and compared with aircraft observations. The initial results indicate that the 3D cloud model is capable of simulating the major features of observed storm systems when given a representative atmospheric sounding to initialize the convective systems. The simulations of infrared and microwave radiances provide reasonably good comparisons with the observations.

Yeh, H.-Y. M.↗
NASA NTRS2003

Surface Penetrating Radar Simulations for Jupiter's Icy Moons

The icy moons of Jupiter (Europa, Callisto, and Ganymede) are of similar overall composition but show different surface features as a result of different sub-surface processes. Furthermore, each of these moons could have a liquid ocean of water buried underneath the icy crust, but their depth can only be speculated. For Europa, estimates put the thickness of the ice shell anywhere between 2-30 km, with'a few models predicting up to 100 km. Much of the uncertainties are due to the largely unknown temperature gradients and levels of water impurities across different surface layers. One of the most important geological processes is the possible transportation of heat by ice convection. If the ice is convecting, then an upper limit of about 20 km is set for the depth of the ocean underneath. Convection leads to a sharp increase in temperature followed by a thick region of nearly constant temperature. If ice is not convecting, then an exponentially increasing temperature profile is expected. The crust is thought to be a mixture of ice and rock, and although the exact percentage of rock is not known, it is expected to be low. Additionally, the ice crust could contain salt, similar to sea ice on Earth. The exact amount of salt and how that amount changes with depth is also unknown. In preparation for the Jupiter Icy Moons Orbiter (JIMO) mission, we performed simulations for a surface-penetrating radar investigating signatures for different possible surface and sub-surface structures of these moons in order to estimate the applicability of using radar with a frequency range between 1 and 50 MHz. This includes simulations of power requirements, attenuation losses, layer resolutions for scenarios with and without the presence of a liquid ocean underneath the ice, cases of convecting and non-convecting ice, different impurities within the ice, and different surface roughnesses.

Markus, Thorsten↗
NASA NTRS1991

Airborne radar simulation studies of the Denver July 11, 1988 microburst

In the simulation program, a wind shear detection Doppler radar was placed in UAL 395 and 236 aircraft and flown along their landing flight paths. The microburst was placed at the appropriate location and intensity corresponding to each aircraft's landing approach time. A baseline set of radar design parameters were used in the simulation. Output display information and wind shear detection processing was produced as the aircraft approached the microburst. Information on the results of the simulation study are given in graphical form.

Britt, Charles L.↗
NASA NTRS2003

Simulated Radar Characteristics of LBA Convective Systems: Easterly and Westerly Regimes

The 3D Goddard Cumulus Ensemble (GCE) model was used to simulate convection that occurred during the TRMM LBA field experiment in Brazil. Convection in this region can be categorized into two different regimes. Low-level easterly flow results in moderate to high CAPE and a drier environment. Convection is more intense like that seen over continents. Low-level westerly flow results in low CAPE and a moist environment. Convection is weaker and more widespread characteristic of oceanic or monsoon-like systems. The GCE model has been used to study both regimes n order to provide cloud datasets that are representative of both environments in support of TRMM rainfall and heating algorithm development. Two different cases are analyzed: Jan 26, 1999, an eastely regime case, and Feb 23, 1999, a westerly regime case. The Jan 26 case is an organized squall line, while the Feb 23 case is less organized with only transient lines. Radar signatures, including CFADs, from the two simulated cases are compared to each other and with observations. The microphysical processes simulated in the model are also compared between the two cases.

Lang, Stephen E.↗
NASA NTRS2015

Benefits of a 4th Ice Class in the Simulated Radar Reflectivities of Convective Systems Using a Bulk Microphysics Scheme

Numerous cloud microphysical schemes designed for cloud and mesoscale models are currently in use, ranging from simple bulk to multi-moment, multi-class to explicit bin schemes. This study details the benefits of adding a 4th ice class (hail) to an already improved 3-class ice bulk microphysics scheme developed for the Goddard Cumulus Ensemble model based on Rutledge and Hobbs (1983,1984). Besides the addition and modification of several hail processes from Lin et al. (1983), further modifications were made to the 3-ice processes, including allowing greater ice super saturation and mitigating spurious evaporationsublimation in the saturation adjustment scheme, allowing graupelhail to become snow via vapor growth and hail to become graupel via riming, and the inclusion of a rain evaporation correction and vapor diffusivity factor. The improved 3-ice snowgraupel size-mapping schemes were adjusted to be more stable at higher mixing rations and to increase the aggregation effect for snow. A snow density mapping was also added. The new scheme was applied to an intense continental squall line and a weaker, loosely-organized continental case using three different hail intercepts. Peak simulated reflectivities agree well with radar for both the intense and weaker case and were better than earlier 3-ice versions when using a moderate and large intercept for hail, respectively. Simulated reflectivity distributions versus height were also improved versus radar in both cases compared to earlier 3-ice versions. The bin-based rain evaporation correction affected the squall line case more but did not change the overall agreement in reflectivity distributions.

bulk microphysics schemes↗
NASA NTRS2004

Surface Penetrating Radar Simulations for Europa

The space environment above the icy surface of Europa is a source of radio noise in this frequency range from natural sources in the Jovian magnetosphere. The ionospheric and magnetospheric plasma environment of Europa affects propagation of transmitted and return signals between the spacecraft and the solid surface in a frequency-dependent manner. The ultimate resolution of the subsurface sounding measurements will be determined, in part, by a capability to mitigate these effects. We discuss an integrated multi-frequency approach to active radio sounding of the Europa ionospheric and local magnetospheric environments, based on operational experience from the Radio Plasma Imaging @PI) experiment on the IMAGE spacecraft in Earth orbit, in support of the subsurface measurement objectives.

Markus, T.↗
NASA NTRS2020

An Evaluation of UAS Pilot Workload and Acceptability Ratings with Four Simulated Radar Declaration Ranges

Currently, minimum operating standards (MOPS) are being developed for a broader range of UAS types, including smaller UAS that will feature onboard sensors that are low in size, weight, and power (Low SWaP). These sensors will have limited declaration ranges compared to ones typically found on medium-to-large UAS used to detect non-cooperative aircraft. A human-in-the-loop (HITL) study was conducted examining four possible radar declaration ranges (i.e., 1.5 nm, 2 nm, 2.5 nm, and 3 nm) for a potential low SWaP sensor with a DAA system. Participants had lower workload, particularly workload associated with temporal demand and effort. Furthermore, participants reported better ability to remain DAA well clear within the larger declaration range conditions, such as the 2.5 nm and 3 nm.

UAS↗
NASA NTRSDate not supplied

An Evaluation of UAS Pilot Workload and Acceptability Ratings with Four Simulated Radar Declaration Ranges

Currently, minimum operational performance standards (MOPS) are being developed for a broader range of unmanned aircraft system (UAS) platforms, including smaller UAS that will feature onboard sensors that are low in size, weight, and power, otherwise known as low SWaP. The low SWaP sensors used to detect non-cooperative traffic will have limited declaration ranges compared to those designed for medium-to-large UAS. A human-in-the-loop (HITL) study was conducted examining four possible radar declaration ranges (i.e., 1.5 NM, 2 NM, 2.5 NM, and 3 NM) for a potential low SWaP sensor with a detect and avoid (DAA) system encountering various non-cooperative encounters in Oakland Center airspace. Participants had lower workload, particularly workload associated with temporal demand and effort, in scenarios that featured larger declaration ranges. Furthermore, participants reported better ability to remain DAA well clear within the larger declaration range conditions, specifically with the 2.5 NM and 3 NM conditions.

UAS↗
NASA NTRS2020

An Evaluation of UAS Pilot Workload and Acceptability Ratings with Four Simulated Radar Declaration Ranges

Currently, minimum operational performance standards (MOPS) are being developed for a broader range of unmanned aircraft system (UAS) platforms, including smaller UAS that will feature onboard sensors that are low in size, weight, and power, otherwise known as low SWaP. The low SWaP sensors used to detect non-cooperative traffic will have limited declaration ranges compared to those designed for medium-to-large UAS. A human-in-the-loop (HITL) study was conducted examining four possible radar declaration ranges (i.e., 1.5 NM, 2 NM, 2.5 NM, and 3 NM) for a potential low SWaP sensor with a detect and avoid (DAA) system encountering various non-cooperative encounters in Oakland Center airspace. Participants had lower workload, particularly workload associated with temporal demand and effort, in scenarios that featured larger declaration ranges. Furthermore, participants reported better ability to remain DAA well clear within the larger declaration range conditions, specifically with the 2.5 NM and 3 NM conditions.

UAS↗