Space Research and Technology Institute

Remote detection and monitoring of the vegetation responses to stress became relevant for sustainable agriculture. Ongoing developments in optical remote sensing technologies have provided tools to increase our understanding of stress-related physiological processes. Therefore, this study aimed to provide an overview of the main spectral technologies and retrieval approaches for detecting crop stress in agriculture. Firstly, we present integrated views on: i) biotic and abiotic stress factors, the phases of stress, and respective plant responses, and ii) the affected traits, appropriate spectral domains and corresponding methods for measuring traits remotely. Secondly, representative results of a systematic literature analysis are highlighted, identifying the current status and possible future trends in stress detection and monitoring. Distinct plant responses occurring under shortterm, medium-term or severe chronic stress exposure can be captured with remote sensing due to specific light interaction processes, such as absorption and scattering manifested in the reflected radiance, i.e. visible (VIS), near infrared (NIR), shortwave infrared, and emitted radiance, i.e. solar-induced fluorescence and thermal infrared (TIR). From the analysis of 96 research papers, the following trends can be observed: increasing usage of satellite and unmanned aerial vehicle data in parallel with a shift in methods from simpler parametric approaches towards more advanced physically-based and hybrid models. Most study designs were largely driven by sensor availability and practical economic reasons, leading to the common usage of VIS-NIR-TIR sensor combinations. The majority of reviewed studies compared stress proxies calculated from single-source sensor domains rather than using data in a synergistic way. We identified new ways forward as guidance for improved synergistic usage of spectral domains for stress detection: (1) combined acquisition of data from multiple sensors for analysing multiple stress responses simultaneously (holistic view); (2) simultaneous retrieval of plant traits combining multi-domain radiative transfer models and machine learning methods; (3) assimilation of estimated plant traits from distinct spectral domains into integrated crop growth models. As a future outlook, we recommend combining multiple remote sensing data streams into crop model assimilation schemes to build up Digital Twins of agroecosystems, which may provide the most efficient way to detect the diversity of environmental and biotic stresses and thus enable respective management decisions.

We present results from the first attempts to derive various physical characteristics of the dusty Wolf–Rayet (WR) star WR 48a based on a multiwavelength view of its observational properties. This is done on the basis of new optical and near-infrared spectral observations and on data from various archives in the optical, radio and X-rays. The optical spectrum of WR 48a is acceptably well represented by a sum of two spectra: of a WR star of the WC8 type and of a WR star of the WN8h type. The strength of the interstellar absorption features in the optical spectra of WR 48a and the near-by stars D2-3 and D2-7 (both members of the open cluster Danks 2) indicates that WR 48a is located at a distance of ∼4 kpc from us. WR 48a is very likely a thermal radio source and for such a case and smooth (no clumps) wind its radio emission suggests a relatively high mass-loss rate of this dusty WR star (⁠|$\dot{M} \approx \mbox{a few} \times 10^{-4}$| M⊙ yr−1). Long time-scale (years) variability of WR 48a is established in the optical, radio and X-rays. Colliding stellar winds likely play a very important role in the physics of this object. However, some luminous blue variable like activity could not be excluded as well.

We analyze four ASCA X-ray observations of the Wolf-Rayet binary system WR 140 obtained between 1993 and 1997 by making use of hydrodynamic colliding wind (CW) shock models. The analysis shows that the CW shock models are able to accurately reproduce the X-ray spectra at different orbital phases using mass-loss and orbital parameters that are within the ranges allowed by the uncertainties. However, some adjustment in the currently accepted values of the semimajor axis and time of periastron passage may eventually be required. Models that allow for different electron and ion temperatures provide better fits to the data. Extra absorption is inferred from CW shock models above that expected from the winds and interstellar medium, the origin of which is not yet known. We also report the serendipitous discovery of hot plasma at temperatures in excess of ~2 keV and X-ray emission lines in spectra extracted from the diffuse Cygnus superbubble background in the vicinity of WR 140.

The red-edge bands of Sentinel-2 allow for a greater diversity of spectral Vegetation Indices (VIs) to be calculated and used for vegetation characterization. We evaluated the utility of a selection of 40 VIs to derive Leaf Area Index (LAI), fraction of Absorbed Photosynthetically Active Radiation (fAPAR) and fraction of vegetation Cover (fCover) of winter wheat crop using regression method. We calibrated models for specific winter wheat development stages and compared the predictions with all-season models. The most useful VIs could be grouped into several types: (1) indices which use green and NIR band, (2) indices based on red edge bands, (3) indices which use red and NIR band and (4) the MCARI/OSAVIre index. It was found that fAPAR and fCover could be predicted with good accuracy using all-season models (rRMSE of 14% and 23% respectively), while LAI showed lower accuracy (rRMSE = 45%). The LAI model calibrated over the tillering stage was recommended for usage in the early stages of crop development. Compared with the existing methods for biophysical variables retrieval from Sentinel-2 data (i.e. the Level2B processor in SNAP) the regression approach based on VIs showed to be a viable alternative.

Abstract The impact of the genotype‐specific leaf morphological and anatomical characteristics on the ability of wheat plants to preserve leaf water balance and cell membranes stability under drought stress was investigated. Seedlings of six modern semi‐dwarf (carriers of Rht, R educed h eigh t genes) and six old tall bread wheat varieties were subjected to soil drought by withholding watering for 6 days. Morpho‐anatomical traits (leaf area, perimeter, thickness, stomata and trichome density) of daily watered (control) plants were characterized by light microscopy, scanning and image analyses. The leaf water status in both control and stressed plants was determined by measuring the relative water content ( RWC ). The leaf cell membranes stability in stressed plants was estimated by conductometric determination of the membranes injury index. On average, the modern semi‐dwarf varieties had less leaf area and leaf perimeter, and less dissection index, a parameter characterizing the leaf shape. Under drought stress, the modern genotypes maintained better water balance evidenced by significantly higher leaf RWC and better‐preserved the cell membranes stability supported by significantly lower Injury index. The correlations between morpho‐anatomical traits in control plants and drought tolerance‐related traits showed that the higher the leaf dissection index (i.e. more oblong leaves), the greater the water loss and the leaf membrane damages after desiccation were. The effect of shape of the evaporating surface on the water loss was modelled using wet filter paper. Similar to plant leaves, the evaporation and, respectively, water loss from paper pieces of more oblong shape (i.e. higher dissection index) was more intensive. The elucidation of the impact of the leaf shape on transpiration might contribute to better understanding of the mechanisms used by plants to maintain water reserves during drought stress and could be a basis for developing of simple and fast screening methods aiding the selection of drought tolerant genotypes.

Abstract The radiation risk radiometer‐dosimeter (R3D)‐R2 solid‐state detector performed radiation measurements at the European Space Agency EXPOSE‐R2 platform outside of the Russian “Zvezda” module at the International Space Station (ISS) from 24 October 2014 to 11 January 2016. The ISS orbital parameters were average altitude of 415 km and 51.6° inclination. We developed special software and used experimentally obtained formulas to determine the radiation flux‐to‐dose ratio from the R3DR2 Liulin‐type deposited‐energy spectrometer. We provide for the first time simultaneous, long‐term estimates of radiation dose external to the ISS for four source categories: (i) galactic cosmic ray particles and their secondary products; (ii) protons in the South Atlantic Anomaly region of the inner radiation belt (IRB); (iii) relativistic electrons and/or bremsstrahlung in the outer radiation belt (ORB); and (iv) solar energetic particle (SEP) events. The latter category is new in this study. Additionally, in this study, secondary particles (SP) resulting from energetic particle interaction with the detector and nearby materials are identified. These are observed continuously at high latitudes. The detected SPs are identified using the same sorting requirements as SEP protons. The IRB protons provide the highest consistent hourly dose, while the ORB electrons and SEPs provide the most extreme hourly doses. SEPs were observed 11 times during the study interval. The R3DR2 data support calculation of average equivalent doses. The 30 day and 1 year average equivalent doses are much smaller than the skin and eyes doses recommendations by the National Council on Radiation Protection (Report 132), which provides radiation protection guidance for Low Earth Orbit.

We discuss the X-ray emission observed from Supernova Remnant 1987A with the Chandra X-ray Observatory. We analyze a high resolution spectrum obtained in 1999 October with the high energy transmission grating (HETG). From this spectrum we measure the strengths and an average profile of the observed X-ray lines. We also analyze a high signal-to-noise ratio CCD spectrum obtained in 2000 December. The good statistics (~ 9250 counts) of this spectrum and the high spatial resolution provided by the telescope allow us to perform spectroscopic analyses of different regions of the remnant. We discuss the relevant shock physics that can explain the observed X-ray emission. The X-ray spectra are well fit by plane parallel shock models with post-shock electron temperatures of ~ 2.6 keV and ionization ages of ~ 6 x 10^10 cm^3/s. The combined X-ray line profile has a FWHM of ~ 5000 km/s, indicating a blast wave speed of ~ 3500 km/s. At this speed, plasma with a mean post-shock temperature of ~ 17 keV is produced. This is direct evidence for incomplete electron-ion temperature equilibration behind the shock. Assuming this shock temperature, we constrain the amount of collisionless electron heating at the shock front at T_e0 / T_s = 0.11 (+0.02,-0.01). We find that the plasma has low metallicity (abundances are ~ 0.1 -- 0.4 solar) and is nitrogen enriched (N/O ~ 0.8 by number), similar to that found for the equatorial ring. Analysis of the spectra from different regions of the remnant reveals slight differences in the parameters of the emitting plasma. The plasma is cooler near the optical Spot 1 (at position angle ~ 30 degrees) and in the eastern half of the remnant, where the bright optical spots are found, than in the western half, consistent with the presence of slower (~ 500 km/s) shocks entering denser ring material.

We report and interpret Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) long-slit observations of the optical and ultraviolet (1150-10270 Å) emission line spectra of the rapidly brightening spot 1 on the equatorial ring of SN 1987A between 1997 September and 1999 October (days 3869-4606 after outburst). The emission is caused by radiative shocks created where the supernova blast wave strikes dense gas protruding inward from the equatorial ring. We measure and tabulate line identifications, fluxes, and, in some cases, line widths and shifts. We compute flux correction factors to account for substantial interstellar line absorption of several emission lines. Nebular analysis shows that optical emission lines come from a region of cool (T e ≈ 10 4 K) and dense (n e ≈ 10 6 cm -3) gas in the compressed photoionized layer behind the radiative shock. The observed line widths indicate that only shocks with shock velocities V s < 250 km s -1 have become radiative, while line ratios indicate that much of the emission must have come from yet slower (V s ≲ 135 km s -1) shocks. Such slow shocks can be present only if the protrusion has atomic density n ≳ 3 × 10 4 cm -3, somewhat higher than that of the circumstellar ring. We are able to fit the UV fluxes with an idealized radiative shock model consisting of two shocks (V s = 135 and 250 km s -1). The observed UV flux increase with time can be explained by the increase in shock surface areas as the blast wave overtakes more of the protrusion. The observed flux ratios of optical to highly ionized UV lines are greater by a factor of ∼2-3 than predictions from the radiative shock models, and we discuss the possible causes. We also present models for the observed Ha line widths and profiles, which suggest that a chaotic flow exists in the photoionized regions of these shocks. We discuss what can be learned with future observations of all the spots present on the equatorial ring.

We present an update on the results of our monitoring observations of the X-ray remnant of supernova (SN) 1987A with the {\it Chandra X-Ray Observatory}. As of 2002 December, we have performed a total of seven observations of SN 1987A. The high angular resolution images from the latest data reveal developments of new X-ray bright spots in the northwestern and the southwestern portions of the remnant as well as changes on the eastern side. The latest 0.5-2 keV band flux ($f_X$ $\sim$ 6 $\times$ 10$^{-13}$ ergs cm$^{-2}$ s$^{-1}$) is four times brighter than three years earlier. The overall X-ray emission is primarily from the blast wave shock with $kT$ $\sim$ 2.4 keV. As the blast wave approaches the dense circumstellar material, the contribution from the decelerated slow shock ($kT$ $\sim$ 0.22 keV) to the observed X-ray emission is becoming significant. The increase of this slow shock contribution over the last two years is particularly noticeable in the western half of the remnant. These results indicate that the shock front is now reaching the main body of the inner circumstellar ring. Based on the best-fit two-shock spectral model, we derive approximate densities of the X-ray-emitting regions ($n_e$ $\sim$ 235 cm$^{-3}$ for the fast shock and $n_e$ $\sim$ 7500 cm$^{-3}$ for the slow shock). We obtain an upper limit on the observed X-ray luminosity of any embedded point source ($L_X$ $\le$ 1.5 $\times$ 10$^{34}$ ergs s$^{-1}$) in the 2$-$10 keV band. The X-ray remnant continues to expand linearly at a rate of 4167 km s$^{-1}$.

30-m Global Land Cover (GLC) data products permit the detection of land cover changes at the scale of most human land activities, and are therefore used as fundamental information for sustainable development, environmental change studies, and many other societal benefit areas. In the past few years, increasing efforts have been devoted to the accuracy assessment of GlobeLand30 and other finer-resolution GLC data products. However, most of them were conducted either within a limited percentage of map sheets selected from a global scale or in some individual countries (areas), and there are still many areas where the uncertainty of 30-m resolution GLC data products remains to be validated and documented. In order to promote a comprehensive and collaborative validation of 30-m GLC data products, the GEO Global Land Cover Community Activity had organized a project from 2015 to 2017, to examine and explore its major problems, including the lack of international agreed validation guidelines and on-line tools for facilitating collaborative validation activities. With the joint effort of experts and users from 30 GEO member countries or participating organizations, a technical specification for 30-m GLC validation was developed based on the findings and experiences. An on-line validation tool, GLCVal, was developed by integrating land cover validation procedures with the service computing technologies. About 20 countries (regions) have completed the accuracy assessment of GlobeLand30 for their territories with the guidance of the technical specification and the support of GLCVal.

We report on the present stage of SN 1987A as observed by the Chandra X-ray Observatory. We reanalyze published Chandra observations and add three more epochs of Chandra data to get a consistent picture of the evolution of the X-ray fluxes in several energy bands. We discuss the implications of several calibration issues for Chandra data. Using the most recent Chandra calibration files, we find that the 0.5-2.0 keV band fluxes of SN 1987A have increased by ~6 x 10 ^-13 erg s^-1 cm^-2 per year since 2009. This is in contrast with our previous result that the 0.5-2.0 keV light curve showed a sudden flattening in 2009. Based on our new analysis, we conclude that the forward shock is still in full interaction with the equatorial ring.

We report an up-turn in the soft X-ray light curve of supernova remnant (SNR) 1987A in late 2003 (~6200 days after the explosion), as observed with the Chandra X-ray Observatory. Since early 2004, the rapid increase of the 0.5-2 keV band X-ray light curve can no longer be described by the exponential density distribution model with which we successfully fitted the data between 1990 and 2003. Around day ~6200, we also find that the fractional contribution to the observed soft X-ray flux from the decelerated shock begins to exceed that of the fast shock and that the X-ray brightening becomes "global" rather than "spotty". We interpret these results as evidence that the blast wave has reached the main body of the dense circumstellar material all around the inner ring. This interpretation is supported by other recent observations, including a deceleration of the radial expansion of the X-ray remnant, a significant up-turn in the mid-IR intensities, and the prevalence of the optical hot spots around the entire inner ring, all of which occur at around day 6000. In contrast to the soft X-ray light curve, the hard band (3-10 keV) X-ray light curve increases at a much lower rate which is rather similar to the radio light curve. The hard X-ray emission may thus originate from the reverse shock where the radio emission is likely produced. Alternatively, the low increase rate of the hard X-rays may simply be a result of the continuous softening of the overall X-ray spectrum.

A brief review of the study during COST Action ES0803 of effects due to cosmic rays (CR) and solar energetic particles (SEP) in the ionosphere and atmosphere is presented. Models CORIMIA (COsmic Ray Ionization Model for Ionosphere and Atmosphere) and application of CORSIKA (COsmic Ray SImulations for KAscade) code are considered. They are capable to compute the cosmic ray ionization profiles at a given location, time, solar and geomagnetic activity. Intercomparison of the models, as well as comparison with direct measurements of the atmospheric ionization, validates their applicability for the entire atmosphere and for the different levels of the solar activity. The effects of CR and SEP can be very strong locally in the polar cap regions, affecting the physical-chemical and electrical properties of the ionosphere and atmosphere. Contributions here were also made by the anomalous CR, whose ionization is significant at high geomagnetic latitudes (above 65°–70°). Several recent achievements and application of CR ionization models are briefly presented. This work is the output from the SG 1.1 of the COST ES0803 action (2008–2012) and the emphasis is given on the progress achieved by European scientists involved in this collaboration.

Annual pollen-accumulation rates (PAR) of Fagus (beech) obtained within the framework of the Pollen Monitoring Programme (PMP) were analyzed in pollen traps along a N–S transect from the Baltic Sea to the Black Sea in different European vegetation units. The study regions are situated in the lowlands of northern Poland, the uplands of SE Poland, the Czech Krkonoše Mts, the Czech Šumava Mts, the Swiss Jura Mts, the Swiss Alps, the Bulgarian Rila Mts and the Bulgarian Strandzha Mts. Most time series are 10 or 11 years long, some are 5–16 years long. Inter-annual fluctuations in Fagus PAR were analyzed and compared with seed mast years. Years with high Fagus PAR and others with low Fagus PAR occurred most frequently in parallel within each region and often in two neighbouring regions. 2006 was exceptional as it had a very high Fagus sylvatica pollen deposition in all study regions and it was also a mast year. In Bulgaria, the trend in the 5 years of Fagus orientalis PAR in the Strandzha Mts differed from that of F. sylvatica PAR in the Rila Mts. Aiming at establishing the relationship between average Fagus PAR and tree cover, differences in Fagus PAR (averaged per pollen trap) were related in each region to the proportion of beech trees in the vegetation within 2 km of the pollen traps, the distance to the nearest pollinating Fagus tree, regional or local presence of beech forests, the degree of landscape openness, and the size of forest opening in which a trap is situated. Average Fagus PAR was found to track the regional abundance of beech trees in the vegetation, not the distance of the nearest Fagus tree. Regional occurrence of beech-dominated forests was reflected by a Fagus PAR of ca. 1,400 grains cm−2 year−1, local abundance very close to pollen traps by ca. 2,400 grains, small patches of forest with admixture of Fagus by ca. 170–220 grains, and scarcity or absence of Fagus by ca. 40 grains or less.

$\sim$18 yr after the supernova explosion, the blast wave of SNR 1987A is entering the main body of the equatorial circumstellar material, which is causing a dramatic brightening of the remnant. We recently reported the observational evidence for this event from our {\it Chandra} data (Park et al. 2005b; P05 hereafter). We present here the temporal evolution of the X-ray emitting shock parameters and the detailed description of the spectral and image analysis of SNR 1987A, on which P05 was based. While the remnant becomes brighter, the softening of the overall X-ray spectrum continues and is enhanced on around day $\sim$6200 (since the explosion). The two-component shock model indicates that the electron temperatures have been changing for the last $\sim$6 yr. The X-ray spectrum is now described by $kT$ $\sim$ 0.3 keV and 2.3 keV thermal plasmas which are believed to characteristically represent the shock-heated density gradient along the boundary between the H{\small II} region and the dense inner ring. As the blast wave sweeps through the inner circumstellar ring shining in X-rays, we expect that the shock parameters continue to change, revealing the density and abundance structure of the inner ring. Follow-up {\it Chandra} observations will thus uncover the past history of the progenitor's stellar evolution. The origin of the relatively faint hard X-ray emission ($E$ $>$ 3 keV) from SNR 1987A is still unclear (thermal vs. nonthermal). Considering the continuous brightening of the hard band intensity, as well as the soft band flux, follow-up monitoring observations will also be essential to reveal the origin of the hard X-ray emission of SNR 1987A.

Abstract The rheology, dc‐conductivity, and microwave properties of acrylic, polyurethane, and epoxy composites containing 0–15 vol % of nanosized carbon particles have been investigated. Carbon nanoparticles (1–3 nm) are produced by a shock wave technology. Steady‐state shear and oscillatory flow tests are applied to investigate the rheological properties of dispersions; dc‐conductivity and MW absorption/reflection are investigated for solid composite films. Rheological characteristics are used for the evaluation of agglomeration processes of nanoparticles in dispersions, as controlled by volume fraction and processing technology. The percolation threshold is interpreted as a structural transition from a dispersed to an agglomerated state and it is found to depend significantly on the type of the matrix polymer. Above the percolation threshold, the presence of carbon nanoparticles produces a strong increase in the viscosity of dispersions as well as of the electrical conductivity and microwave properties of solid composites. A good correlation between the three characteristics is found for the systems in a wide range of carbon volume fractions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2220–2227, 2004

The present concept on the origin of X-rays in massive OB stars posits that they are emitted by hot gas heated by shocks (Lucy & White 1980; Lucy 1982). OB stars possess massive and fast winds driven by radiation

Abstract. Vegetation productivity is a critical indicator of global ecosystem health and is impacted by human activities and climate change. A wide range of optical sensing platforms, from ground-based to airborne and satellite, provide spatially continuous information on terrestrial vegetation status and functioning. As optical Earth observation (EO) data are usually routinely acquired, vegetation can be monitored repeatedly over time, reflecting seasonal vegetation patterns and trends in vegetation productivity metrics. Such metrics include gross primary productivity, net primary productivity, biomass, or yield. To summarize current knowledge, in this paper we systematically reviewed time series (TS) literature for assessing state-of-the-art vegetation productivity monitoring approaches for different ecosystems based on optical remote sensing (RS) data. As the integration of solar-induced fluorescence (SIF) data in vegetation productivity processing chains has emerged as a promising source, we also include this relatively recent sensor modality. We define three methodological categories to derive productivity metrics from remotely sensed TS of vegetation indices or quantitative traits: (i) trend analysis and anomaly detection, (ii) land surface phenology, and (iii) integration and assimilation of TS-derived metrics into statistical and process-based dynamic vegetation models (DVMs). Although the majority of used TS data streams originate from data acquired from satellite platforms, TS data from aircraft and unoccupied aerial vehicles have found their way into productivity monitoring studies. To facilitate processing, we provide a list of common toolboxes for inferring productivity metrics and information from TS data. We further discuss validation strategies of the RS data derived productivity metrics: (1) using in situ measured data, such as yield; (2) sensor networks of distinct sensors, including spectroradiometers, flux towers, or phenological cameras; and (3) inter-comparison of different productivity metrics. Finally, we address current challenges and propose a conceptual framework for productivity metrics derivation, including fully integrated DVMs and radiative transfer models here labelled as “Digital Twin”. This novel framework meets the requirements of multiple ecosystems and enables both an improved understanding of vegetation temporal dynamics in response to climate and environmental drivers and enhances the accuracy of vegetation productivity monitoring.

Titanium dioxide (TiO2) thin films have generated considerable interest over recent years, because they are functional materials suitable for a wide range of applications. The efficient use of the outstanding functional properties of these films relies strongly on their basic characteristics, such as structure and morphology, which are affected by deposition parameters. Here, we report on the influence of plasma power and precursor chemistry on the growth kinetics, structure and morphology of TiO2 thin films grown on Si(100) by plasma-enhanced atomic layer deposition (PEALD). For this, remote capacitively coupled 13.56 MHz oxygen plasma was used to act as a co-reactant during the ALD process using two different metal precursors: titanium tetrachloride (TiCl4) and titanium tetraisopropoxide (TTIP). Furthermore, we investigate the effect of direct plasma exposure during the co-reactant pulse on the aforementioned material properties. The extensive characterization of TiO2 films using Rutherford backscattering spectroscopy, ellipsometry, x-ray diffraction (XRD), field-emission scanning electron microscopy, and atomic force microscopy (AFM) have revealed how the investigated process parameters affect their growth per cycle (GPC), crystallization and morphology. The GPC tends to increase with plasma power for both precursors, however, for the TTIP precursor, it starts decreasing when the plasma power is greater than 100 W. From XRD analysis, we found a good correlation between film crystallinity and GPC behavior, mainly for the TTIP process. The AFM images indicated the formation of films with grain size higher than film thickness (grain size/film thickness ratio ≈20) for both precursors, and plasma power analysis allows us to infer that this phenomenon can be directly related to the increase of the flux of energetic oxygen species on the substrate/growing film surface. Finally, the effect of direct plasma exposure on film structure and morphology was evidenced showing that the grid removal causes a drastic reduction in the grain size, particularly for TiO2 synthesized using TiCl4.

We discuss the results from deep Chandra LETG observations of the supernova remnant 1987A (SNR 1987A). We find that a distribution of shocks, spanning the same range of velocities (from 300 to 1700 km/s) as deduced in the first part of our analysis (Zhekov et al. 2005, ApJL, 628, L127), can account for the entire X-ray spectrum of this object. The post-shock temperature distribution is bimodal, peaking at kT 0.5 and 3 keV. Abundances inferred from the X-ray spectrum have values similar to those for the inner circumstellar ring, except that the abundances of nitrogen and oxygen are approximately a factor of two lower than those inferred from the optical/UV spectrum. The velocity of the X-ray emitting plasma has decreased since 1999, apparently because the blast wave has entered the main body of the inner circumstellar ring.