True Surface Temperature Research Articles

Space-time multi-level modeling for zooplankton abundance employing double data fusion and calibration

An important objective for marine biologists is to forecast the distribution and abundance of planktivorous marine predators. To do so, it is critically important to understand the spatiotemporal dynamics of their prey. Here, the prey we study are zooplankton and we build a novel space-time hierarchical fusion model to describe the distribution and abundance of zooplankton species in Cape Cod Bay (CCB), MA, USA. The data were collected irregularly in space and time at sites within the first half of the year over a 17 year period, using two different sampling methods. We focus on sea surface zooplankton abundance and incorporate sea surface temperature as a primary driver, also collected with two different sampling methods. So, with two sources for each, we observe true abundance or true sea surface temperature with measurement error. To account for such error, we apply calibrations to align the data sources and use the fusion model to develop a prediction of daily spatial zooplankton abundance surfaces throughout CCB. To infer average abundance on a given day within a given year in CCB, we present a marginalization of the zooplankton abundance surface. We extend the inference to consider abundance averaged to a bi-weekly or annual scale as well as to make an annual comparison of abundance.

Hourly road pavement surface temperature forecasting using deep learning models

Road authorities in cold climates regularly apply salt on roads, during winter, to ensure public safety. Pavement surface temperature is a significant parameter affecting snow and ice melting at the onset of a storm. Road temperature below the freezing point of the applied brine causes ice to form on the road surface. Excessive application of salt on the road can have adverse environmental impacts, especially to soil and water quality. Therefore, forecasting pavement temperature can optimize road salt application, while reducing costs, improving public safety, and reducing environmental impacts. This research aims to develop a reliable and accurate pavement surface temperature prediction tool using machine learning techniques. This study employs advanced deep neural network (DNN) learning techniques to predict pavement surface temperature for road salt management purposes. To validate the proposed methodology, this work used hourly solar radiation and air temperature data from Environment Canada, and pavement surface temperature data collected from the Road Weather Information System (RWIS), for sites around the city of Toronto, Ontario. The performance of the proposed DNN model, that integrates a Convolutional Neural Network (CNN) with a Long Short-Term Memory (LSTM), on pavement surface temperature forecasting, was evaluated against four other comparative machine learning methods, LSTM, Convolutional-LSTM (ConvLSTM), Sequence-to-Sequence (Seq2Seq), and Wavelet neural network (Wavenet) models. A dataset of 10,895 samples was collected as an hourly pavement surface temperature record in three timeframes from November 2009 to March 2014 on Highway 401 in southern Ontario, Canada. Experiments included predictions for 1-, 2-, 4- and 6-hours ahead, using as input features air temperature, solar radiation, and present pavement temperature. The proposed pavement temperature forecasting approach resulting from this investigation suggests our new approach is more accurate than previous models. These results reveal that the CNN-LSTM outperforms the four other models and creates predictions closer to the true pavement surface temperature.

Multi-spectral temperature measurement based on adaptive emissivity model under high temperature background

When the object surface temperature in high temperature environment is measured by multi-spectral temperature measurement method, the radiation generated by the reflection of the high temperature background on the surface of the object and the radiation emitted by the object itself are both received by the pyrometer. For one thing, the amount of radiation received by the pyrometer increases. On the other hand, the surface emissivity model may change. So a large temperature measurement error may occur. In order to accurately measure the true surface temperature of an object in a high temperature environment, a multi-spectral temperature measurement method based on adaptive emissivity model is proposed in this paper. First, BP neural network is used to identify the shape of spectral data and obtain the correspondence between spectral data and emissivity model, then output the emissivity model that conforms to the measured target and specific environment. Moreover, the traditional NSGA-II algorithm (Non-dominant sorting genetic algorithm-II) is prone to falling into local optimal solutions and the numerical values obtained are not accurate enough. In this paper, the concepts of clustering algorithm, difference operator and symmetrical solution are introduced in the process of crossover and mutation, and then the new algorithm of INSGA-II (Improved Non-dominant sorting genetic algorithm-II)) is proposed. On the basis of this algorithm, the emissivity model of BP network is combined to solve the target true temperature. The experimental results show that the maximum temperature measurement error can reach 60 K if the influence of high temperature background is ignored. After removing the influence of high temperature background, the non-adaptive emissivity model was used to obtain the maximum temperature error of 30 K, and the fluctuation between adjacent temperature points was large. The multi-spectral temperature measurement method based on adaptive emissivity model proposed in this paper can obtain more accurate temperature measurement results with the maximum error of 8 K.

Inverse radiation problem with infrared images to monitor plasma-facing components temperature in metallic fusion devices

Abstract Infrared (IR) diagnostics are used to measure plasma-facing components (PFC) surface temperature in fusion devices. However, the interpretation of such images is complex in all-reflective environments because of unknown emissivity and multiple reflections issues. In order to assess these challenges an iterative inversion method based on a fast photonic model, the radiosity method, has been developed. The radiosity method is based on strong hypotheses including all diffuse surfaces. The inversion method allows retrieving the true surface temperature of PFC in two steps: a step of the target emissivity estimation in a baking scene and the use of the emissivity map to retrieve the temperature of metallic components with errors up to 3% during a plasma scenario.

Methodology for High-Accuracy Infrared Calibration in Environments with Through-Wall Heat Flux

This paper describes a new method for accurate in situ infrared (IR) calibration in environments with significant through-wall heat flux and surface temperature non-uniformity. In the context of turbine research environments, conventional approaches for in situ IR calibrations rely on thermocouples embedded in the surface or bonded to the surface using an adhesive layer. A review of the literature points to lack of emphasis on the uncertainty in the calibration arising from the effect of the adhesive substrate and paint on the temperature measured by the thermocouple, namely that under diabatic conditions (i.e. with through-wall heat flux) the measured temperature deviates from the true surface temperature. We present a systematic study of the sensitivity of the thermocouple temperature to installation conditions seen in typical laboratory IR calibration arrangements, and under realistic conditions of through-wall heat flux. A new technique is proposed that improves the calibration accuracy by reducing the difference between the thermocouple measurement and the external wall temperature seen by the infrared camera. The new technique has the additional advantage of reducing the uncertainty associated with selecting an appropriate pixel in the IR image, by providing a region with greater temperature uniformity especially in environments with significant underlying lateral surface temperature variation. The new approach is experimentally demonstrated and compared to more conventional measurement techniques on a heavily film-cooled nozzle guide vane assembly operated at highly engine-representative conditions. The proposed technique is demonstrated to significantly improve the measurement accuracy for IR in situ calibrations in environment with through-wall heat flux and surface temperature non-uniformity.

3D thermography for improving temperature measurements in thermal vacuum testing

The application of thermography to thermal vacuum (TV) testing of spacecrafts is becoming a vital additional tool in the mapping of structures during thermal cycles and thermal balance (TB) testing. Many of the customers at the European Space Agency (ESA) test centre, European Space Research and Technology Centre (ESTEC), The Netherlands, now make use of a thermal camera during TB-TV campaigns. This complements the use of embedded thermocouples on the structure, providing the prospect of monitoring temperatures at high resolution and high frequency. For simple flat structures with a well-defined emissivity, it is possible to determine the surface temperatures with reasonable confidence. However, for most real spacecraft and sub-systems, the complexity of the structure’s shape and its test environment creates inter-reflections from external structures. This and the additional complication of angular and spectral variations of the spacecraft surface emissivity make the interpretation of the radiation detected by a thermal camera more difficult in terms of determining a validated temperature with high confidence and well-defined uncertainty. One solution to this problem is: to map the geometry of the test specimen and thermal test environment; to model the surface temperatures and emissivity variations of the structures and materials; and to use this model to correct the apparent temperatures recorded by the thermal camera. This approach has been used by a team from NPL (National Physical Laboratory), Psi-tran, and PhotoCore, working with ESA, to develop a 3D thermography system to provide a means to validate thermal camera temperatures, based on a combination of thermal imaging photogrammetry and ray-tracing scene modeling. The system has been tested at ESTEC in ambient conditions with a dummy spacecraft structure containing a representative set of surface temperatures, shapes, and spacecraft materials, and with hot external sources and a high power lamp as a sun simulator. The results are presented here with estimated temperature measurement uncertainties and defined confidence levels according to the internationally accepted Guide to Uncertainty of Measurement as used in the IEC/ISO17025 test and measurement standard. This work is understood to represent the first application of well-understood thermal imaging theory, commercial photogrammetry software, and open-source ray-tracing software (adapted to realize the Planck function for thermal wavebands and target emission), and to produce from these elements a complete system for determining true surface temperatures for complex spacecraft-testing applications.

Development of Two-color Radiation Thermometer for Harsh Environments

Many industrial processes require reliable temperature measurements in harsh environments with high temperature, dust, humidity, and pressure. However, commercially-available conventional temperature measurement devices are not suitable for use in such conditions. This study thus proposes a reliable, durable two-color radiation thermometer (RT) for harsh environments that was developed by selecting the appropriate components, designing a suitable mechanical structure, and compensating environmental factors such as absorption by particles and gases. The two-color RT has a simple, compactly-designed probe with a well-structured data acquisition system combined with efficient LabVIEW-based code. As a result, the RT can measure the temperature in real time, ranging from 300 to <TEX>$900^{\circ}C$</TEX> in extremely harsh environments, such as that above the burden zone of a blast furnace. The error in the temperature measurements taken with the proposed two-color RT compared to that obtained using K-type thermocouple readouts was within 6.1 to <TEX>$1.4^{\circ}C$</TEX> at a temperature range from 200 to <TEX>$700^{\circ}C$</TEX>. The effects of absorption by gases including <TEX>$CO_2$</TEX>, CO and <TEX>$H_2O$</TEX> and the scattering by fine particles were calculated to find the transmittance of the two wavelength bands of operation through the path between the measured burden surface and the two-color probe. This method is applied to determine the transmittance of the short and long wavelength bands to be 0.31 and 0.51, respectively. Accordingly, the signals that were measured were corrected, and the true burden surface temperature was calculated. The proposed two-color RT and the correction method can be applied to measure temperatures in harsh environments where light-absorbing gases and scattering particles exist and optical components can be contaminated.

A method for improving temperature measurement precision on the uncooled infrared thermal imager

In order to improve temperature measurement precision of the uncooled infrared thermal imager, aiming at the influence of the thermal imager internal radiation, a method is proposed based on voltage compensation in this paper. Firstly, combining the principle of uncooled infrared thermal imager, radiation of tested object is converted to voltage values, the voltage values are converted to grey value can be measured, and thus the relationship between radiation of tested object and grey value is established. Secondly, according to the relationship between radiation and grey value, a model about uncooled infrared thermal imager temperature measurement is established. A formula for computing the true surface temperature of objects is given. Coefficients are acquired in the temperature measurement formula by collecting the infrared image data of standard blackbody. Finally, in order to verify the correctness of the compensation method, an experiment about blackbody is conducted in this paper. The experiment results show that this method can effectively reduce the relative error of the thermal imager temperature measurement.

What is responsible for the strong observed asymmetry in teleconnections between El Niño and La Niña?

AbstractA large asymmetric component (El Niño + La Niña) of El Niño–Southern Oscillation (ENSO)‐related teleconnections over North America is found during 1984–2009 that is comparable in strength to the commonly studied symmetric component (El Niño − La Niña). Climate reforecasts spanning this period are diagnosed in order to understand the processes responsible for the observed asymmetry. It is confirmed that an asymmetric component is indeed a fundamental property of atmospheric responses to recent ENSO forcing. Each and every composite of a 16‐member reforecast ensemble has appreciable asymmetry in tropical Pacific rainfall, upper tropospheric Pacific‐North American circulation patterns, and contiguous U.S. surface temperatures. There is considerable sampling variability in the magnitude of this asymmetric component among individual reforecast composites. We argue therefore that the true sea surface temperature boundary‐forced signal of ENSO teleconnections is likely composed of a symmetric component having greater magnitude than its asymmetric component, though the latter is an important property of how ENSO affects North American climate.

Primary spectrum pyrometry based on radiation measurement within a finite solid angle

The true surface temperature for an object can be determined by measuring emitted radiation. Primary spectrum pyrometry should be generally carried out by radiation measurement within an infinitesimal solid angle or within a finite solid angle in the case of diffuse emission, so that the radiation thermometry equations become a closed system for temperature and other undetermined parameters. The radiation thermometry equation with linear emissivity model is obtained, which can be used to measure the temperature of the object with non-diffuse emission within a finite solid angle. This equation is universal in radiation measurement, based on which equations for primary spectrum pyrometry are deduced. These equations are also universal in radiation measurement, in which the emissivity scales under different measurement conditions are limited to the same range, but have different physical meanings.

Problems in measuring the temperature of conductors heated by an electric current pulse

Different methods are considered for measuring the temperature of conductors heated by an electric current pulse. Special attention is given to optical methods. Ways are discussed of designing blackbody models, including those developed recently for measuring the temperature under pulsed heating of small objects to 5000 K and above. New methods are described for high-speed measurement of the true surface temperature of conductors, namely, laser polarimetry and reflectometry. These methods do not require the use of blackbody model for measuring and investigating the dependence of spectral emissivity on the rate of heating and cooling. The possibility is analyzed of the emergence of specific error in measurements of the temperature of rapidly heated objects, which is due to deviation of the process from thermodynamic equilibrium and, as a result, to the shift of the registered melting temperature with respect to equilibrium.

Multidimensional Assessment of Modeling Error in Typical High-Speed Wind-Tunnel Heat-Transfer Data-Reduction Schemes

R IGOROUS validation of computational tools places stringent demands on the accuracy of measured experimental data. This is increasingly the case in fluid dynamics, in which computational approaches havematured to the point at which certain propertiesmay be predicted to the same level of accuracy that can be measured. In such a situation, a discrepancy between computation and experiment cannot simply be assumed to lie exclusively in either the computational or experimental result. Rather, a thorough evaluation of both the computational and experimental techniques is required. Such is the case for perfect-gas wind-tunnel measurements of surface heat transfer for a simple body in an attached laminar flow. A standard technique for measuring the heat-transfer rate to a surface is via thermocouple instrumentation. The thermocouples may be subjected to an unknown heat flux for some period of time, and temperature histories may be obtained. This surface temperature history can then be used as a boundary condition in a transient thermal analysis from which the heat-transfer rate may be inferred. This technique is often employed in wind-tunnel tests that seek to quantify the aerothermodynamic environment for a given geometry. In such applications, the thermocouple instrumentation is typically too sparse to determine a true multidimensional surface temperature distribution, which could then be used in a three-dimensional thermal analysis. Consequently, the thermocouple temperature histories are often used in conjunction with a one-dimensional heat-transfer analysis, which only considers conduction normal to the surface. For geometries with regions of tight curvature and/or substantial lateral gradients in heat-flux distribution, the validity of the onedimensional assumption comes into question. This Note investigates the modeling error induced by the combined factors of lateral heat-flux distribution and multidimensional curvature for a specific geometry that was recently tested in the Arnold Engineering Development Center’s Hypervelocity Wind Tunnel no. 9. A purely analytical approach is used that combines steady computational fluid dynamics simulation, transient threedimensional thermal analysis, and the standard transient onedimensional thermal analysis technique to quantify the modeling error introduced through the data-reduction process for each gauge. The remainder of the Note is organized as follows: Section II provides an overview of the experimental test series that provides the motivation for this work, Sec. III describes the analytical approach used to predict the external convective heat-transfer and the transient thermal analysis, Sec. IV presents results for the specific case of a scaled Orion Crew Module model at wind-tunnel conditions, and some general conclusions are discussed in Sec. V.

Optically accessible channel reactor for the kinetic investigation of hydrocarbon reforming reactions

A new experimental reactor concept for studying heterogeneously catalyzed gas phase reactions was developed, which allows true surface temperature measurements along the reactor through a quartz window without affecting the flow in the reactor using IR thermography. The catalyst is coated as a thin layer onto a metal plate. The laminar flow field is similar to the one in a monolith channel. A small stream of gas can be withdrawn with a moveable capillary to measure the concentration profile in the reactor. The spatial resolution of the gas sampling is ≤0.1 mm. Two- and three-dimensional fluid dynamic modeling of the channel reactor was performed to check the velocity field in the channel for different operating conditions. Buoyancy forces were insignificant at the conditions studied; the parabolic inlet flow profile was maintained along the reactor channel. The heat loss by radiation from the quartz glass top surface was found to be three times larger than the heat loss by free convection. The methanation of carbon monoxide and carbon dioxide was studied at 550 and 500 °C, respectively. For these reactions nearly isothermal conditions were observed. The partial oxidation of methane, performed without diluting the feed, was also studied at 500 and 550 °C. The measured hot spots correlated well with the concentration profile measurements. Film diffusional limitations were found only significant for the oxidation reaction.

Examination of the Merged Sea Surface Temperature Using Wavelet Analysis

In the previous study, merged sea surface temperature (SST) dataset called “New Generation SST” has been produced from several infrared and microwave satellite SSTs through an objective mapping. Here we examine the merged SST by comparison with moored buoy SST at 1 m depth, which is treated as true sea surface temperature. Comparison between wavelet spectra of merged and buoy SSTs shows that the former have larger amplitudes than those of the latter, which is partly explained as an aliasing effect due to TRMM Microwave Imager (TMI) aboard Tropical Rainfall Measuring Mission (TRMM) sampling on merged products. Coherency between wavelet-decomposed merged and buoy SSTs has high values in autumn and low ones in winter to spring. In winter, phase differences between them are positive, meaning that wavelet components of merged SST lag those of buoy SST. Reasons for delay and low coherency are: (1) seasonal components of merged SSTs are strongly affected by a lack of infrared SSTs due to clouds in winter, and (2) small-scale oceanic features, undetectable by coarse-resolution microwave SSTs, are blurred by the merging process. Improvements of merging methodology are discussed with regard to present study results.

The analysis of optimization criteria for multi-band pyrometry

This paper presents a new radiation pyrometry, multi-band pyrometry, obtained by increasing the narrow wavelength bandwidth of multi-wavelength pyrometry. The purpose of this paper is to evaluate the necessity for and the merit of multi-band pyrometry, compared with the traditional multi-wavelength pyrometry. Here, we propose theoretical optimization criteria, based on the temperature discrimination resolution, to analyse the characteristics of multi-band pyrometry. The simulation results indicate that the wavelength bandwidth of multi-band pyrometry does affect the temperature discrimination resolution, and the choice of the bandwidth range will have a significant influence on the performance of the radiation pyrometer. Finally, we conclude that the traditional multi-wavelength pyrometry with ‘pure’ wavelengths is sometimes not the optimum method for measurements of true surface temperatures. However, multi-band pyrometry with the appropriate bandwidth range may be the optimum method to achieve optimum measurements.

Miniature Thermal Emission Spectrometer for the Mars Exploration Rovers

The Miniature Thermal Emission Spectrometer (Mini‐TES) will provide remote measurements of mineralogy and thermophysical properties of the scene surrounding the Mars Exploration Rovers and guide the rovers to key targets for detailed in situ measurements by other rover experiments. The specific scientific objectives of the Mini‐TES investigation are to (1) determine the mineralogy of rocks and soils, (2) determine the thermophysical properties of selected soil patches, and (3) determine the temperature profile, dust and water‐ice opacity, and water vapor abundance in the lower atmospheric boundary layer. The Mini‐TES is a Fourier Transform Spectrometer covering the spectral range 5–29 μm (339.50 to 1997.06 cm−1) with a spectral sample interval of 9.99 cm−1. The Mini‐TES telescope is a 6.35‐cm‐diameter Cassegrain telescope that feeds a flat‐plate Michelson moving mirror mounted on a voice‐coil motor assembly. A single deuterated triglycine sulfate (DTGS) uncooled pyroelectric detector with proven space heritage gives a spatial resolution of 20 mrad; an actuated field stop can reduce the field of view to 8 mrad. Mini‐TES is mounted within the rover's Warm Electronics Box and views the terrain using its internal telescope looking up the hollow shaft of the Pancam Mast Assembly (PMA) to the fixed fold mirror and rotating elevation scan mirror in the PMA head located ∼1.5 m above the ground. The PMA provides a full 360°of azimuth travel and views from 30° above the nominal horizon to 50° below. An interferogram is collected every two seconds and transmitted to the Rover computer, where the Fast Fourier Transform, spectral summing, lossless compression, and data formatting are performed prior to transmission to Earth. Radiometric calibration is provided by two calibration V‐groove blackbody targets instrumented with platinum thermistor temperature sensors with absolute temperature calibration of ±0.1°C. One calibration target is located inside the PMA head; the second is on the Rover deck. The Mini‐TES temperature is expected to vary diurnally from −10 to +30°C, with most surface composition data collected at scene temperatures &gt;270 K. For these conditions the radiometric precision for two‐spectra summing is ±1.8 × 10−8 W cm−2 sr−1/cm−1 between 450 and 1500 cm−1, increasing to ∼4.2 × 10−8 W cm−2 sr−1/cm−1 at shorter (300 cm−1) and longer (1800 cm−1) wave numbers. The absolute radiance error will be &lt;5 × 10−8 W cm−2 sr−1/cm−1, decreasing to ∼1 × 10−8 W cm−2 sr−1/cm−1 over the wave number range where the scene temperature will be determined (1200–1600 cm−1). The worst‐case sum of these random and systematic radiance errors corresponds to an absolute temperature error of ∼0.4 K for a true surface temperature of 270 K and ∼1.5 K for a surface at 180 K. The Mini‐TES will be operated in a 20‐mrad panorama mode and an 8‐mrad targeted mode, producing two‐dimensional rasters and three‐dimensional hyperspectral image cubes of varying sizes. The overall Mini‐TES envelope size is 23.5 × 16.3 × 15.5 cm, and the mass is 2.40 kg. The power consumption is 5.6 W average. The Mini‐TES was developed by Arizona State University and Raytheon Santa Barbara Remote Sensing.

Automated emissivity corrected wafer-temperature measurement in Aixtrons planetary reactors

A procedure and set-up for high-precision determination of the true surface temperature of wafers during growth by metalorganic vapour phase epitaxy is described. The reflectance of the surface measured by an EpiRAS ® sensor is used for correcting the signal of a pyrometer for changes in emissivity. This allows for determination of the true surface temperature with a precision of ±1°C even for multilayer structures. This high precision allows to determine differences in the temperature of wafers of different size or rotating at different speed in an Aixtron Planetary Reactor ®.

Accurate measurement and interpretation of the heat flux to the divertor in TEXT Upgrade

To obtain accurate measurements of the heat flux to divertor tiles for comparison with probe data in the SOL and with models, digitized infrared camera data were calibrated and corrected for tile emissivity to provide true tile surface temperatures. The surface temperature T(x,y,t) was analysed with a full three dimensional heat flux code, including temperature dependent thermal properties, to extract the heat flux to the divertor tiles in the TEXT Upgrade tokamak. Each of the complexities in the analysis proved necessary for precise results. The parallel heat flux at the separatrix was generally consistent with independently measured edge parameters: a sheath transmission coefficient of ∼5 is inferred. The flux to the tiles varied with cosθinc as expected. The decay length for heat flux in the SOL did not vary significantly with conditions and remained ∼2.5 mm (traced to the outer midplane), which is significantly shorter than that implied by density and temperature scale lengths in the SOL.

Ultra-fast optical pyrometry for the measurement of detonating explosive temperature

This paper describes a multiwavelength optical pyrometer designed to measure, with a 3 ns rise-time, the evolution of a fast varying temperature as can be encountered in the detonation products of an explosive. By measuring six luminance temperatures within the visible and near infra-red spectra, this apparatus allows to determine a true surface temperature over the range 1500 to 6000 K. It has been used for studies of detonation in nitromethane, a transparent liquid explosive.

A conceptual model for effective directional emissivity from nonisothermal surfaces

The conventional definition of emissivity requires the source of radiation to be isothermal in order to compare its thermal emission to that of a blackbody at the same temperature. This requirement is not met for most land surfaces considered in thermal infrared remote sensing. Thus, the effective or equivalent emissivity of nonisothermal surfaces has been a poorly defined but widely used concept for years. Recently, several authors have attempted to define this concept more clearly. Unfortunately, definitions such as ensemble emissivity (e-emissivity) and emissivity derived from the surface bidirectional reflectance distribution function (r-emissivity), J. Norman et al. (1995), do not fully satisfy current needs for estimating true land surface temperature (LST). The present authors suggest the use of an additional term, the "apparent emissivity increment", which considers the effects of geometric optics to explain the directional and spectral dependence in LST caused by the three-dimensional (3D) structure and subpixel temperature distribution of the surface. They define this quantity based upon the emissivity derived from the bidirectional reflectance distribution function (/spl epsi//sub BRDF/) for isothermal surfaces and present a conceptual model of thermal emission from nonisothermal land surfaces. Their study also indicates that an average LST corresponding to the hemispherical wideband /spl epsi//sub BRDF/ Will be useful in remote sensing-based LST modeling and inversion.