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NASA NTRS1993

Preliminary results from multiparameter airborne rain radar measurement in the western Pacific

Preliminary results are presented from multiparameter airborne radar measurements of tropical storms. The experiment was conducted in the western Pacific in September 1990 with the NASA DC-8 aircraft that was equipped with a dual-wavelength radar at X and Ka bands and several microwave radiometers. The modification to dual-polarization at X-band radar enabled measurements of the linear depolarization ratio (LDR). Vertical profiles of dual-polarization and dual-frequency observables for an example of stratiform rain and three examples of convective rain cells are examined. It is shown that at nadir incidence the LDR measurement often can be used to distinguish the phase states of the hydrometeors and to identify the melting layer. In addition to the information concerning particle shape and orientation from LDR, the ratio of the radar reflectivity factors in two frequency bands (X and Ka bands) provides insight into particle size. The capabilities of dual-wavelength and dual-polarization radar in the identification of particle size and phase will be important considerations in the design of future spaceborne weather radars.

Kumagai, Hiroshi↗

DOE OSTI2026

Volumetric Subtractive Manufacturing

Manufacturing small negative features has been extremely challenging in whole additive manufacturing (AM) field. Due to overcuring, diffusion and refractive index increase, the achievable smallest negative feature and fidelity is always worse than the smallest positive one using AM methods. Additionally, attempting to print multi-scale feature sizes in the same exposure has proven to be challenging in DLP printing due to diffusion and inhibition. To address these challenges, we have developed a hybrid additive and subtractive manufacturing approach on a DLP platform with a dual-wavelength photopolymers to be able to print multi-scale features and small negative features with accuracy. And we also have demonstrated a first-of-its-kind Volumetric Subtractive Manufacturing by fabricating non-planar double helix fluidics by photo-degrading polymers. This work has the potential to shift the paradigm of DLP AM techniques by incorporating subtractive manufacturing as a new degree of freedom for enhancing the achievable print resolution and enabling corrective and adaptive manufacturing.

42 ENGINEERING↗

DOE OSTI2026

Understanding spectral dependance of laser-induced damage precursors in dielectric materials (Full report_23-ERD-006)

The performance of high-energy laser systems is constrained by laser-induced damage in dielectric coatings, particularly those containing hafnium oxide (HfO 2 ). While thresholds at fundamental Nd harmonics are well studied, the spectral dependence of damage initiation—especially under dual-wavelength irradiation—remains poorly characterized. This project provides the first systematic investigation of wavelength-dependent laser damage in hafnia coatings, focusing on nanoscale precursors such as craze lines, nanobubbles, stoichiometric variations, nodules, and controlled crystallization. Coatings were fabricated via ion beam sputtering and electron-beam deposition and characterized using spectrophotometry, ellipsometry, AFM, GI-XRD, RBS, PCI absorption, and fs/ns laser damage testing. Results show that craze lines, benign under infrared light, strongly initiate damage under UV due to wavelength-selective field intensification. Substituting xenon for argon suppresses nanobubbles and improves UV thresholds by up to 32%. Oxygen modulation reveals that fully oxidized films maximize UV resistance, though at the cost of porosity and stress in multilayers. HfO 2 –SiO 2 composites resist crystallization and defects while achieving ppm-level absorption and elevated thresholds, whereas full crystallization of HfO 2 enhances LIDT by reducing defects and improving thermal transport. Collectively, these findings link photon energy, defect states, and bandgap collapse, providing a predictive framework for wavelength-dependent laser damage. The outcomes directly inform the design of durable, multi-wavelength coatings for facilities such as NIF, MEC, HAPLS, and DPAL, advancing the readiness of next-generation optics.

36 MATERIALS SCIENCE↗

NASA NTRS1972

Two-laser optical distance-measuring instrument that corrects for the atmospheric index of refraction.

The Wave Propagation Laboratory of the Environmental Research Laboratories of the National Oceanic and Atmospheric Administration has been engaged in the development of dual-wavelength, optical distance-measuring instruments. Recently a new generation of this type of high-accuracy instrument has been completed. Preliminary testing of the new instrument indicates that the original goal of the project, accuracy of better than one part in a million over distances of 5-10 km using averaging times of less than 1 min, is being met. This paper describes the instrument and preliminary test results.

Earnshaw, K. B.↗

NASA NTRS1975

Carbon dioxide sensor

Analytical techniques for measuring CO2 were evaluated and rated for use with the advanced extravehicular mobility unit. An infrared absorption concept using a dual-wavelength monochromator was selected for investigation. A breadboard carbon dioxide sensor (CDS) was assembled and tested. The CDS performance showed the capability of measuring CO2 over the range of 0 to 4.0 kPa (0 to 30 mmHg) P sub (CO2). The volume and weight of a flight configured CDS should be acceptable. It is recommended that development continue to complete the design of a flight prototype.

Source record↗

NASA NTRS1983

Experimental comparison of heterodyne and direct detection for pulsed differential absorption CO2 lidar

A pulsed dual-wavelength dual-CO2-laser differential-absorption lidar (DIAL) system has been developed which permits simultaneous heterodyne and direct detection of the same lidar returns. This system has been used to make an experimental comparison of the SNRs and statistical and temporal characteristics of the DIAL returns from several topographic targets. These results were found to be in general agreement with theory and were used to quantify the relative merits of the two detection techniques. The measured parameter values were applied to an analytical treatment to predict system trade-offs for the remote sensing of atmospheric species, with application to both path-averaged and range-resolved measurements.

Killinger, D. K.↗

NASA NTRS1983

Radio scintillations observed during atmospheric occultations of Voyager: Internal gravity waves at Titan and magnetic field orientations at Jupiter and Saturn

The refractive index of planetary atmospheres at microwave frequencies is discussed. Physical models proposed for the refractive irregularities in the ionosphere and neutral atmosphere serve to characterize the atmospheric scattering structures, and are used subsequently to compute theoretical scintillation spectra for comparison with the Voyager occultation measurements. A technique for systematically analyzing and interpreting the signal fluctuations observed during planetary occultations is presented and applied to process the dual-wavelength data from the Voyager radio occultations by Jupiter, Saturn, and Titan. Results concerning the plasma irregularities in the upper ionospheres of Jupiter and Saturn are reported. The measured orientation of the irregularities is used to infer the magnetic field direction at several locations in the ionospheres of these two planets; the occultation measurements conflict with the predictions of Jovian magnetic field models, but generally confirm current models of Saturn's field. Wave parameters, including the vertical fluxes of energy and momentum, are estimated, and the source of the internal gravity waves discovered in Titan's upper atmosphere is considered.

Hinson, D. P.↗

NASA NTRS1985

Prospects for altimetry and scatterometry in the 90's

Current NASA plans for altimetry and scatterometry of the oceans using spaceborne instrumentation are outlined. The data of interest covers geostrophic and wind-driven circulation, heat content, the horizontal heat flux of the ocean, and the interactions between atmosphere and ocean and ocean and climate. A proposed TOPEX satellite is to be launched in 1991, carrying a radar altimeter to measure the ocean surface topography. Employing dual-wavelength operation would furnish ionospheric correction data. Multibeam instruments could also be flown on the multiple-instrument polar orbiting platforms comprising the Earth Observation System. A microwave radar scatterometer, which functions on the basis of Bragg scattering of microwave energy off of wavelets, would operate at various view angles and furnish wind speeds accurate to 1.5 m/sec and directions accurate to 20 deg.

Townsend, W. F.↗

NASA NTRS1985

Nd:YAG and ruby based lidar systems for remote sensing of atmospheric aerosols

The application of solid-state lasers to the study of stratospheric and tropospheric aerosols is analyzed. A 48-inch mobile lidar which operates in the 0.6943, 1.06, 0.3472, and 0.5300 micron ranges is utilized to monitor the stratosphere. The detectors of the system consist of photomultipliers, and the dual-channel, computer-based data-acquisition-system which provides on-line plotting of scattering ratio profiles. The components of the 14-inch aperture, dual-wavelength airborne lidar system that operates with ruby and Nd:YAG transmitters are described. An 8-inch, down-looking airborne lidar with silicon diode or photomultiplier detectors was developed. The capabilities of the system alone and when combined with the 14-inch lidar are discussed. Examples of the data provided by the three lidar systems are presented, revealing the reliability and operational efficiency of the systems.

Fuller, W. H., Jr.↗

NASA NTRS1990

Range profiling of the rain rate by an airborne weather radar

A class of methods based on a measure of path attenuation that is used to constrain the Hitschfeld-Bordan solution is investigated. Such methods are investigated for lidar, radar, and combined radar-radiometer applications. Their function is to allocate the attenuation in proportion to the strength of the measured reflectivity. A description is provided of four estimates of rain rate that have been tested using data from a dual-wavelength airborne radar at 10 GHz and 35 GHz. It is concluded, that when attenuation is significant, the estimates are generally more accurate than those without attenuation correction. Thus, such methodologies can be utilized to extend the effective dynamic range of the radar to higher rain rates.

Meneghini, Robert↗

NASA NTRS1991

STROZ LITE - Stratospheric Ozone Lidar Trailer Experiment

A mobile dual-wavelength differential absorption lidar capable of making precise measurements of stratospheric ozone between 20 and 45 km has been developed at the Goddard Space Flight Center as part of the international Network for the Detection of Stratospheric Change. The system is installed in a 46-ft trailer, which enables the instrument to act as a network transfer standard and to be set up at any location where power can be obtained. A description of the instrument is presented, along with a discussion of the data analysis. Some results from an intercomparison held at JPL's Table Mountain Observatory in California during October and November 1988 are also presented.

Mcgee, Thomas J.↗

NASA NTRS1990

Spaceborne weather radar

The present work on the development status of spaceborne weather radar systems and services discusses radar instrument complementarities, the current forms of equations for the characterization of such aspects of weather radar performance as surface and mirror-image returns, polarimetry, and Doppler considerations, and such essential factors in spaceborne weather radar design as frequency selection, scanning modes, and the application of SAR to rain detection. Attention is then given to radar signal absorption by the various atmospheric gases, rain drop size distribution and wind velocity determinations, and the characteristics of clouds, as well as the range of available estimation methods for backscattering, single- and dual-wavelength attenuation, and polarimetric and climatological characteristics.

Meneghini, Robert↗

NASA NTRS1992

Polarization-stabilized 1.15- and 3.39-micron He-Ne lasers

Two methods for polarization stabilization of an internal-mirror 3.39-micron He-Ne laser are reported. The first relies on a concurrently lasing 1.15-micron transition by fixing the relative amplitude of two orthogonally polarized longitudinal modes that are split by a Rochon prism and detected with separate Si photodiodes. In the second method, two spatially separated orthogonally polarized adjacent 3.39-micron modes are optically balanced, differentially chopped, and recombined on a single InSb photodiode for phase-sensitive detection. The dual-wavelength scheme has been tested by beating against a methane-stabilized 3.39-micron He-Ne laser, which yields maximum excursions of less than 0.5 MHz over several hours and comparable reproducibility. The polarization-stabilized He-Ne laser has been used as a reference for a tunable color-center laser molecular-beam optothermal spectrometer and provides a precision of better than 2 MHz.

Junttila, M.-L.↗

NASA NTRS1993

First radar echoes from cumulus clouds

In attempting to use centimeter-wavelength radars to investigate the early stage of precipitation formation in clouds, 'mantle echoes' are rediscovered and shown to come mostly from scattering by small-scale variations in refractive index, a Bragg kind of scattering mechanism. This limits the usefulness of single-wavelength radar for studies of hydrometeor growth, according to data on summer cumulus clouds in North Dakota, Hawaii, and Florida, to values of reflectivity factor above about 10 dBZe with 10-cm radar, 0 dBZe with 5-cm radar, and -10 dBZe with 3-cm radar. These are limits at or above which the backscattered radar signal from the kinds of clouds observed can be assumed to be almost entirely from hydrometeors or (rarely) other particulate material such as insects. Dual-wavelength radar data can provide the desired information about hydrometeors at very low reflectivity levels if assumptions can be made about the inhomogeneities responsible for the Bragg scattering. The Bragg scattering signal itself probably will be a useful way to probe inhomogeneities one-half the radar wavelength in scale for studying cloud entrainment and mixing processes. However, this use is possible only before scattering from hydrometeors dominates the radar return.

Knight, Charles A.↗

NASA NTRS1992

Dual-polarization characteristics of the radar ocean return in the presence of rain

Experimental data are presented on the polarimetric and dual-wavelength characteristics of the ocean surface in the presence of rain. To explain a portion of the variability observed in scatter plots under rain conditions, a storm model is used that incorporates measured drop size distributions. The fairly large variability indicates that effects of drop size distribution and the presence of partially melted particles can introduce a significant error in the estimate of attenuation. This effect is especially significant in the case of a 10-GHz radar under high rain rates. A surface reference method at this frequency will tend to overestimate the rain attenuation unless melting layer attenuation is properly taken into account. Observations of the cross-polarization return in stratiform rain over an ocean surface show three distinct components. Two of these correspond to aspherical, nonaligned particles in the melting layer seen in the direct and mirror-image returns. The remaining part depends both on the off-nadir depolarization by the surface and on the rain medium. A possible mechanism for this latter effect is the bistatic scattering from the rain to the surface.

Meneghini, R.↗

NASA NTRS1992

Hydrometeor discrimination in melting layer using multiparameter airborne radar measurement

Results from a multiparameter airborne radar/radiometer experiment (the Typhoon experiment) are presented. The experiment was conducted in the western Pacific with the NASA DC-8 aircraft, in which a dual-wavelength at X-band and Ka-band and dual-polarization at X-band radar was installed. The signatures of dBZ(X), dBZ(Ka), LDR (linear depolarization ratio) at X-band and DZ=dBZ(X)-dBZ(Ka) are discussed for the data obtained in the penetration of the typhoon Flo. With emphasis on discrimination of hydrometeor particles, some statistical features of the brightband in stratiform rain are discussed.

Kumagai, H.↗

NASA NTRS1992

Radar depolarization signatures of rain in cumulus clouds measured with a dual-frequency air-borne radar

Experimental data are presented on dual-wavelength scattering characteristics of subtropical rain observed during the convection and precipitation/electrification (CaPE) experiment. Linear depolarization ratios (LDRs) are calculated at both X-band and Ka-band channels. In stratiform rain, the cross-polarized return signal is generally below the noise level except within the melting layer where the maximum LDR at both frequencies is typically between -12 and -10 dB. In convective rain the range profiles of the LDR in X-band and those in Ka-band do not coincide. The X-band LDR values in convective rain typically remain smaller than -25 dB at high altitudes and take somewhat larger values of -25 to -15 dB at low altitudes. The Ka-band LDR values, in contrast, typically increase with radar range, sometimes reaching a level of -3 dB just before the cross-polarized signal falls below the noise level. Such high values of LDR in Ka-band are most likely attributable to multiple scattering effects.

Iguchi, Toshio↗

NASA NTRS1993

GLRS-R 2-colour retroreflector target design and predicted performance

This paper reports on the retroreflector ground-target design for the GLRS-R spaceborne dual-wavelength laser ranging system. The described passive design flows down from the requirements of high station autonomy, high global FOV (up to 60 degrees zenith angle), little or no multiple pulse returns, and adequate optical cross section for most ranging geometries. The proposed solution makes use of 5 hollow cube-corner retroreflectors of which one points to the zenith and the remaining four are inclined from the vertical at uniform azimuthal spacings. The need for fairly large (is approximately 10 cm) retroreflectors is expected (within turbulence limitations) to generate quite narrow diffraction lobes, thus placing non-trivial requirements on the vectorial accuracy of velocity aberration corrections. A good compromise solution is found by appropriately spoiling just one of the retroreflector dihedral angles from 90 degrees, thus generating two symmetrically oriented diffraction lobes in the return beam. The required spoil angles are found to have little dependence on ground target latitude. Various link budget analyses are presented, showing the influence of such factors as point-ahead optimization, turbulence, ranging angle, atmospheric visibility and ground target thermal deformations.

Lund, Glenn↗