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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 73 records · Page 4
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NASA NTRS2020

RainCube and its legacy for the next generation of spaceborne cloud and precipitation radars

The multidimensional challenge of observing cloud and precipitation processes from space has motivated and focused a number of technological developments in the last decade. They span from novel compact instrument architectures to modular millimeter wave phased array solutions. In this paper we summarize the main capabilities offered by three instruments from this new generation, and discuss how they affect formulation of future observing systems.

Rodriguez-Monje, Raquel↗
NASA NTRS2017

RainCube, a Ka-band Precipitation Radar in a 6U CubeSat

RainCube (Radar in a CubeSat) is a 6U CubeSat mission between the Jet Propulsion Laboratory (JPL) and Tyvak Nano-Satellite Systems (Tyvak). The objective of the mission is to develop, launch, and operate a 35.75 GHz nadirpointing precipitation profiling radar payload to validate a new architecture for Ka-band radars and an ultra-compact deployable Ka-band antenna design in the space environment. RainCube will also demonstrate the feasibility of a radar payload on a CubeSat platform. The radar payload is the evolution of two previous JPL research and development technologies – the miniaturized Ka-band atmospheric radar (miniKaAR) and the 0.5m diameter Ka-band parabolic deployable antenna (KaPDA). JPL has contracted Tyvak to develop the spacecraft bus, integrate the payload, and operate the spacecraft. RainCube is currently in integration and test with an expected ready-for-delivery in September 2017.

Williams, Austin↗
NASA NTRS2012

Recent Observations of Clouds and Precipitation by the Airborne Precipitation Radar 2nd Generation in Support of the GPM and ACE Missions

In this paper we illustrate the unique dataset collected during the Global Precipitation Measurement Cold-season Precipitation Experiment (GCPEx, US/Canada Jan/Feb 2012). We will focus on the significance of these observations for the development of algorithms for GPM and ACE, with particular attention to classification and retrievals of frozen and mixed phase hydrometeors.

radar↗
NASA NTRS2008

Advanced Precipitation Radar Antenna to Measure Rainfall From Space

To support NASA s planned 20-year mission to provide sustained global precipitation measurement (EOS-9 Global Precipitation Measurement (GPM)), a deployable antenna has been explored with an inflatable thin-membrane structure. This design uses a 5.3 5.3-m inflatable parabolic reflector with the electronically scanned, dual-frequency phased array feeds to provide improved rainfall measurements at 2.0-km horizontal resolution over a cross-track scan range of up to 37 , necessary for resolving intense, isolated storm cells and for reducing the beam-filling and spatial sampling errors. The two matched radar beams at the two frequencies (Ku and Ka bands) will allow unambiguous retrieval of the parameters in raindrop size distribution. The antenna is inflatable, using rigidizable booms, deployable chain-link supports with prescribed curvatures, a smooth, thin-membrane reflecting surface, and an offset feed technique to achieve the precision surface tolerance (0.2 mm RMS) for meeting the low-sidelobe requirement. The cylindrical parabolic offset-feed reflector augmented with two linear phased array feeds achieves dual-frequency shared-aperture with wide-angle beam scanning and very low sidelobe level of -30 dB. Very long Ku and Ka band microstrip feed arrays incorporating a combination of parallel and series power divider lines with cosine-over-pedestal distribution also augment the sidelobe level and beam scan. This design reduces antenna mass and launch vehicle stowage volume. The Ku and Ka band feed arrays are needed to achieve the required cross-track beam scanning. To demonstrate the inflatable cylindrical reflector with two linear polarizations (V and H), and two beam directions (0deg and 30deg), each frequency band has four individual microstrip array designs. The Ku-band array has a total of 166x2 elements and the Ka-band has 166x4 elements with both bands having element spacing about 0.65 lambda(sub 0). The cylindrical reflector with offset linear array feeds reduces the complexity from "NxN" transmit/receive (T/R) modules of a conventional planar-phased array to just "N" T/R modules. The antenna uses T/R modules with electronic phase-shifters for beam steering. The offset reflector does not provide poor cross-polarization like a double- curved offset reflector would, and it allows the wide scan angle in one plane required by the mission. Also, the cylindrical reflector with two linear array feeds provides dual-frequency performance with a single, shared aperture. The aperture comprises a reflective surface with a focal length of 1.89 m and is made from aluminized Kapton film. The reflective surface is of uniform thickness in the range of a few thousandths of an inch and is attached to the chain-link support structure via an adjustable suspension system. The film aperture rolls up, together with the chain-link structure, for launch and can be deployed in space by the deployment of the chain-link structure.

Rahmat-Samii, Yahya↗
NASA NTRS2012

Recent observations of clouds and precipitation by the Airborne Precipitation Radar 2nd Generation in support of the GPM and ACE missions

In this paper we illustrate the unique dataset collected during the Global Precipitation Measurement Cold-season Precipitation Experiment (GCPEx, US/Canada Jan/Feb 2012). We will focus on the significance of these observations for the development of algorithms for GPM and ACE, with particular attention to classification and retrievals of frozen and mixed phase hydrometeors.

Im, Eastwood↗
NASA NTRS2011

An Experimental Study of the Rainfall Variability Within TRMM/GPM Precipitation Radar and Microwave Sensor Instantaneous Field of View During MC3E

Dual tipping bucket gauges were operated at 16 sites in support of ground based precipitation measurements during Mid-latitude Continental Convective Clouds Experiment (MC3E). The experiment is conducted in North Central Oklahoma from April 22 through June 6, 2011. The gauge sites were distributed around Atmospheric Radiation Measurement (ARM) Climate Research facility where the minimum and maximum separation distances ranged from 1 to 12 km. This study investigates the rainfall variability by employing the stretched exponential function. It will focus on the quantitative assessment of the partial beam of the experiment area in both convective and stratiform rain. The parameters of the exponential function will also be determined for various events. This study is unique for two reasons. First is the existing gauge setup and the second is the highly convective nature of the events with rain rates well above 100 mm h-1 for 20 minutes. We will compare the findings with previous studies.

Tokay, Ali↗
NASA NTRS2011

An Experimental Study of the Rainfall Variability Within TRMM/GPM Precipitation Radar and Microwave Sensor Instantaneous Field of View During MC3E

Dual tipping bucket gauges were operated at 16 sites in support of ground based precipitation measurements during Mid-latitude Continental Convective Clouds Experiment (MC3E). The experiment is conducted in North Central Oklahoma from April 22 through June 6, 2011. The gauge sites were distributed around Atmospheric Radiation Measurement (ARM) Climate Research facility where the minimum and maximum separation distances ranged from 1 to 12 km. This study investigates the rainfall variability by employing the stretched exponential function. It will focus on the quantitative assessment of the partial beam of the experiment area in both convective and stratiform rain. The parameters of the exponential function will also be determined for various events. This study is unique for two reasons. First is the existing gauge setup and the second is the highly convective nature of the events with rain rates well above 100 mm/h for 20 minutes. We will compare the findings with previous studies.

Tokay, Ali↗
NASA NTRS2017

MCRadar: A Monte Carlo Solver for Cloud and Precipitation Radar

Multiple scattering produces anomalous echoes in observed radar profiles that cannot be explained by other phenomena. These effects are most obvious for spaceborne platforms, at shorter wavelengths, and in convection, as multiple scattering is governed by antenna beam width, optical depth, and albe do; however, multiple scattering has been observed in a range of precipitating conditions. To account for the effects of multiple scattering, Monte Carlo integration is employed in a flexible framework to enable arbitrary radar configurations with finite Gaussian beams for three-dimensional atmospheric scenarios. The three-dimensional nature of the model, coupled with the finite antenna response, also allows for consideration of nonuniform beam filling effects that often coincide with multiple scattering. Examples of airborne and spaceborne radars at various wavelengths are used to illustrate the effects of multiple scattering and nonuniform beam filling. The MCRadar code is currently available in the development version of ARTS.

Adams, Ian Stuart↗
NASA NTRS1981

Spaceborne precipitation radar

The performances and characteristics of a satelliteborne radar operating in the millimeter wavelength region of the spectrum with emphasis placed on the 35 and 94 GH3 frequency bands are discussed. It is concluded that millimetric wavelengths provide an acceptable solution for the design of satelliteborne active microwave equipment.

Eckerman, J.↗
NASA NTRS1999

The TRMM Precipitation Radar: Opportunities and Challenges

Although studies on the feasibility of spaceborne weather radar date back to the 1960's, it was only with the launch of the Tropical Rainfall Measuring Mission (TRMM) Satellite in November 1997 that the first weather radar was placed into low earth orbit. The long delay between the initial concept and implementation was caused not only by the demanding requirements of active sensors such as mass, power, and reliability, but because of scientific and technological challenges. For example, the demand for adequate spatial resolution arises from the need to resolve the horizontal structure of convective storm cells and to avoid surface contamination of the rain return at off-nadir angles. To achieve a horizontal resolution on the order of 4 km from low earth orbit with a modest antenna size of 2 m requires the use of a much higher frequency (Ku-band) than those typically used for ground-based weather radars (S- and C-band). Higher frequencies are subject to higher attenuation. As Hitschfeld and Bordan (1954) showed in their classic paper, attenuation correction with a single-wavelength radar is inherently unstable at high attenuations unless the drop size distribution and the radar constant are known precisely. Since these conditions are seldom met, much work over the last decade has been devoted to formulating and testing alternative methods of attenuation correction. The operational method used in the TRMM radar processing is discussed in section 3 of the paper.

Meneghini, R.↗