Engineering topics

Fischer, Erich M.

Publications and source records attributed to Fischer, Erich M..

8 records

DOE OSTI2023

Storylines for unprecedented heatwaves based on ensemble boosting

Recent temperature extremes have shattered previously observed records, reaching intensities that were inconceivable before the events. Could the possibility of an event with such unprecedented intensity as the 2021 Pacific Northwest heatwave have been foreseen, based on climate model information available before the event? Could the scientific community have quantified its potential intensity based on the current generation of climate models? Here, we demonstrate how an ensemble boosting approach can be used to generate physically plausible storylines of a heatwave hotter than observed in the Pacific Northwest. We also show that heatwaves of much greater intensities than ever observed are possible in other locations like the Greater Chicago and Paris regions. In order to establish confidence in storylines of ‘black swan’-type events, different lines of evidence need to be combined along with process understanding to make this information robust and actionable for stakeholders.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2020

Development of Future Heatwaves for Different Hazard Thresholds

In 2018 and 2019, heatwaves set all-time temperature records around the world and caused adverse effects on human health, agriculture, natural ecosystems, and infrastructure. Often, severe impacts relate to the joint spatial and temporal extent of the heatwaves, but most research so far focuses either on spatial or temporal attributes of heatwaves. Furthermore, sensitivity of heatwaves characteristics to the choice of the heatwave thresholds in a warming climate are rarely discussed. Here, we analyze the largest spatiotemporal moderate heatwaves—that is, three-dimensional (space-time) clusters of hot days—in simulations of global climate models. We use three different hazard thresholds to define a hot day: fixed thresholds (time-invariant climatological thresholds), seasonally moving thresholds based on changes in the summer means, and fully moving thresholds (hot days defined relative to the future climatology). We find a substantial increase of spatiotemporally contiguous moderate heatwaves with global warming using fixed thresholds, whereas changes for the other two hazard thresholds are much less pronounced. In particular, no or very little changes in the overall magnitude, spatial extent, and duration are detected when heatwaves are defined relative to the future climatology using a temporally fully moving threshold. This suggests a dominant contribution of thermodynamic compared to dynamic effects in global climate model simulations. The similarity between seasonally moving and fully moving thresholds indicates that seasonal mean warming alone can explain large parts of the warming of extremes. The strong sensitivity of simulated future heatwaves to hazard thresholds should be considered in the projections of potential future heat-related impacts.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1994

Remote determination of exposure degree and iron concentration of lunar soils using VIS-NIR spectroscopic methods

On the Moon, space weathering processes such as micrometeorite bombardment alter the optical properties of lunar soils. As a consequence, lunar soil optical properties are a function not only of composition, but of degree of exposure on the lunar surface as well. In order to accurately assess the compositional properties of the lunar surface using remotely acquired visible and near-infrared spectroscopic data, it is thus necessary either (1) to compare optical properties only of soils characterized by similar degrees of exposure or (2) to otherwise normalize or remove the optical effects due to exposure. Laboratory spectroscopic data for lunar soils are used to develop and test remote spectrocopic methods for determining degree of exposure and for distinguishing between the optical effects due to exposure and those due to composition. A method employing a ratio between reflectances within and outside of the 1 micrometer Fe(2+) crystal field absorption band was developed for remotely identifying highland soils that have reached a steady-state maturity. The relative optical properties of these soils are a function solely of composition and as such can be directly compared. Spectroscopic techniques for accurate quantitative determination of iron content for lunar highland soils are investigated as well. It is shown that approximations of the 1 micrometer Fe(2+) absorption band depth using few to several channel multispectral data or spectroscopic data of inadequate spectral range cannot be used with confidence for compositional analysis. However, band depth measurements derived from continuum-removed high spectral resolution data can be used to calculate the weight percent FeO and relative proportion of iron-bearing silicates in mature lunar highland and mare/highland mixture soils. A preliminary effort to calibrate telescopic band depth to laboratory soil measurements is described.

Fischer, Erich M.↗

NASA NTRS1993

The continuum slope of Mars - Bidirectional reflectance investigations and applications to Olympus Mons

Two primary causes of near-IR continuum slope variations have been observed in an investigation of the bidirectional reflectance characteristics of ferric coatings on the continuum slope of Mars. First, the presence of a thin ferric coating on a dark substrate produces a negative continuum slope due to the wavelength-dependent transparency of the ferric coating. Second, wavelength-dependent directional reflectance occurs when the surface particles are tightly packed, particle sizes are on the order of or smaller than the wavelength of light, or the surface is otherwise smooth on the order of the wavelength of light. Based on these results, the annuli on the flanks of Olympus Mons which are defined by reflectance and continuum slope are consistent with spatial variations in surface texture and possibly with spatial variations in the thickness of a ferric dust coating or rind.

Fischer, Erich M.↗

NASA NTRS1993

Measuring and distinguishing compositional and maturity properties of lunar soils by remote VIS-NIR spectroscopy

Space weathering on the lunar surface affects the spectra/optical character of an exposed lunar soil in three ways: the reflectance is reduced, absorption band depths are reduced, and a red-sloped continuum is created and increased with exposure. As a result, the spectrum of a lunar soil is dependent upon both the degree of exposure at the lunar surface and the original composition. It is critical to the remote analysis of lunar soils to differentiate between the optical effects of maturity and the effects of composition. In the laboratory, it is possible to determine and consequently distinguish the degree of exposure, or soil maturity, as measured by parameters such as I(sub s)/FeO (e.g., 1; mature defined as I(sub s)/FeO greater than or equal to 60), and the composition, as measured by various chemical and petrographical techniques. Lunar soils returned by the Apollo missions provide important ground truth for developing methods for remotely measuring the maturity and the concentration of Fe-bearing minerals in lunar soil. The ground truth spectral data analyzed are from the John Adams lunar soil spectra collection. Soils collected from or near highland terrains are emphasized in the discussion. The mineralogical makeup of mare soils results in behavior somewhat different from highland soils.

Fischer, Erich M.↗

NASA NTRS1992

Lunar Resources Using Moderate Spectral Resolution Visible and Near-infrared Spectroscopy: Al/si and Soil Maturity

Modern visible and near-infrared detectors are critically important for the accurate identification and relative abundance measurement of lunar minerals; however, even a very small number of well-placed visible and near-infrared bandpass channels provide a significant amount of general information about crucial lunar resources. The Galileo Solid State Imaging system (SSI) multispectral data are an important example of this. Al/Si and soil maturity will be discussed as examples of significant general lunar resource information that can be gleaned from moderate spectral resolution visible and near-infrared data with relative ease. Because quantitative-albedo data are necessary for these kinds of analyses, data such as those obtained by Galileo SSI are critical. SSI obtained synoptic digital multispectral image data for both the nearside and farside of the Moon during the first Galileo Earth-Moon encounter in December 1990. The data consist of images through seven filters with bandpasses ranging from 0.40 microns in the ultraviolet to 0.99 microns in the near-infrared. Although these data are of moderate spectral resolution, they still provide information for the following lunar resources: (1) titanium content of mature mare soils based upon the 0.40/0.56-micron (UV/VIS) ratio; (2) mafic mineral abundance based upon the 0.76/0.99-micron ratio; and (3) the maturity or exposure age of the soils based upon the 0.56-0.76-micron continuum and the 0.76/0.99-micron ratio. Within constraints, these moderate spectral resolution visible and near-infrared reflectance data can also provide elemental information such as Al/Si for mature highland soils.

Fischer, Erich M.↗

NASA NTRS1991

Crustal heterogeneity of the moon viewed from the Galileo SSI camera: Lunar sample calibrations and compositional implications

Summaries are given of the spectral calibration, compositional parameters, nearside color, and limb and farside color of the Moon. The farside of the Moon, a large area of lunar crust, is dominated by heavily cratered terrain and basin deposits that represent the products of the first half billion years of crustal evolution. Continuing analysis of the returned lunar samples suggest a magma ocean and/or serial magmatism model for evolution of the primordial lunar crust. However, testing either hypothesis requires compositional information about the crustal stratigraphy and lateral heterogeneity. Resolution of this important planetary science issue is dependent on additional data. New Galileo multispectral images indicate previously unknown local and regional compositional diversity of the farside crust. Future analysis will focus on individual features and a more detailed assessment of crustal stratigraphy and heterogeneity.

Pieters, Carle M.↗

NASA NTRS1991

The perplexing continuum slope of Mars: Effects of thin ferric coatings and viewing geometry

The experiment discussed here was designed to constrain interpretations of variations in continuum slope variations which define several spectral annuli on the flanks of Olympus Mons, observed in the Imaging Spectrometer (IMS) data. The IMS Olympus Mons data reveal that the rings, seen as alternating brighter and darker reflectance in Viking data, correspond to annuli of alternating shallower and steeper continuum slope. At least three factors contributing to continuum slope are identified: ferric coating thickness, viewing geometry, and surface texture. Because the Olympus Mons spectral annuli were observed at nearly constant backscatter geometries in the ISM data, with only slight viewing variations due to the volcanoe's flank slopes, the difference of continuum slope between annuli probably cannot be explained by viewing geometry alone. This suggests that the variation of some fundamental surface characteristics, such as ferric dust/rind thickness or surface texture, is the cause of the Olympus Mons special annuli observed in the ISM imaging spectrometer data.

Fischer, Erich M.↗