Infrared Scan Radiometer Research Articles

Sea Surface Skin Temperature Retrieval from FY-3C/VIRR

The visible and infrared scanning radiometer (VIRR) onboard the Fengyun-3C (FY-3C) meteorological satellite has 11 μm and 12 μm channels, which are capable of sea surface temperature (SST) observations. This study is based on atmospheric radiative transfer modeling (RTM) by applying Bayesian cloud detection theory and optimal estimation (OE) to obtain sea surface skin temperature (SSTskin) from VIRR in the Northwest Pacific. The inter-calibration of FY-3C/VIRR 11 μm and 12 μm brightness temperature (BT) is carried out using the Moderate Resolution Imaging Spectroradiometer (MODIS) as the reference sensor. Bayesian cloud detection and OE SST retrieval with the calibration BT data is performed to obtain SSTskin. The SSTskin retrievals are compared with the buoy SST with a temporal window of 1 h and a spatial window of 0.01°. The bias is −0.12 °C, and the standard deviation is 0.52 °C. Comparisons of the retrieved SSTskin with the AVHRR (Advanced Very High Resolution Radiometer) SSTskin from European Space Agency Sea Surface Temperature Climate Change Initiative (ESA SST CCI) project show the bias of 0.08 °C and the standard deviation of 0.55 °C. The results indicate that the VIRR SSTskin are consistent with AVHRR SSTskin and buoy SST.

Sea Surface Temperature Analysis for Fengyun-3C Data Using Oriented Elliptic Correlation Scales.

Sea surface temperature (SST) is critical for global climate change analysis and research. In this study, we used visible and infrared scanning radiometer (VIRR) sea surface temperature (SST) data from the Fengyun-3C (FY-3C) satellite for SST analysis, and applied the Kalman filtering methods with oriented elliptic correlation scales to construct SST fields. Firstly, the model for the oriented elliptic correlation scale was established for SST analysis. Secondly, observation errors from each type of SST data source were estimated using the optimal matched datasets, and background field errors were calculated using the model of oriented elliptic correlation scale. Finally, the blended SST analysis product was obtained using the Kalman filtering method, then the SST fields using the optimum interpolation (OI) method were chosen for comparison to validate results. The quality analysis for 2016 revealed that the Kalman analysis with a root-mean-square error (RMSE) of 0.3243 °C had better performance than did the OI analysis with a RMSE of 0.3911 °C, which was closer to the OISST product RMSE of 0.2897 °C. The results demonstrated that the Kalman filtering method with dynamic observation error and background error estimation was significantly superior to the OI method in SST analysis for FY-3C SST data.

Retrieval of Sea Surface Wind Fields Using Multi-Source Remote Sensing Data

Timely and accurate sea surface wind field (SSWF) information plays an important role in marine environmental monitoring, weather forecasting, and other atmospheric science studies. In this study, a piecewise linear model is proposed to retrieve SSWF information based on the combination of two different satellite sensors (a microwave scatterometer and an infrared scanning radiometer). First, the time series wind speed dataset, extracted from the HY-2A satellite, and the brightness temperature dataset, extracted from the FY-2E satellite, were matched. The piecewise linear regression model with the highest R2 was then selected as the best model to retrieve SSWF information. Finally, experiments were conducted with the Usagi, Fitow, and Nari typhoons in 2013 to evaluate accuracy. The results show that: (1) the piecewise linear model is successfully established for all typhoons with high R2 (greater than 0.61); (2) for all three cases, the root mean square error () and mean bias error (MBE) are smaller than 2.2 m/s and 1.82 m/s, which indicates that it is suitable and reliable for SSWF information retrieval; and (3) it solves the problem of the low temporal resolution of HY-2A data (12 h), and inherits the high temporal resolution of the FY-2E data (0.5 h). It can provide reliable and high temporal SSWF products.

Radiometric Model and Inter-Comparison Results of the SGLI-VNR On-Board Calibration

The Second Generation Global Imager (SGLI) on Global Change Observation Mission–Climate (GCOM-C) satellite empowers surface and atmospheric measurements related to the carbon cycle and radiation budget, with two radiometers of Visible and Near Infrared Radiometer (SGLI-VNR) and Infrared Scanning Radiometer (SGLI-IRS) that perform a wide-band (380 nm–12 µm) optical observation not only with as wide as a 1150–1400 km field of view (FOV), but also with as high as 0.25–0.5 km resolution. Additionally, polarization and along-track slant view observations are quite characteristic of SGLI. It is important to calibrate radiometers to provide the sensor data records for more than 28 standard products and 23 research products including clouds, aerosols, ocean color, vegetation, snow and ice, and other applications. In this paper, the radiometric model and the first results of on-board calibrations on the SGLI-VNR, which include weekly solar and light-emitting diode (LED) calibration and monthly lunar calibration, will be described. Each calibration data was obtained with corrections, where beta angle correction and avoidance of reflection from multilayer insulation (MLI) were applied for solar calibration; LED temperature correction was performed for LED calibration; and the GIRO (GSICS (Global Space-based Inter-Calibration System) Implementation of the ROLO (RObotic Lunar Observatory) model) model was used for lunar calibration. Results show that the inter-comparison of the relative degradation amount between these three calibrations agreed to within 1% or less.

Half a century of satellite remote sensing of sea-surface temperature

Sea-surface temperature (SST) was one of the first ocean variables to be studied from earth observation satellites. Pioneering images from infrared scanning radiometers revealed the complexity of the surface temperature fields, but these were derived from radiance measurements at orbital heights and included the effects of the intervening atmosphere. Corrections for the effects of the atmosphere to make quantitative estimates of the SST became possible when radiometers with multiple infrared channels were deployed in 1979. At the same time, imaging microwave radiometers with SST capabilities were also flown. Since then, SST has been derived from infrared and microwave radiometers on polar orbiting satellites and from infrared radiometers on geostationary spacecraft. As the performances of satellite radiometers and SST retrieval algorithms improved, accurate, global, high resolution, frequently sampled SST fields became fundamental to many research and operational activities. Here we provide an overview of the physics of the derivation of SST and the history of the development of satellite instruments over half a century. As demonstrated accuracies increased, they stimulated scientific research into the oceans, the coupled ocean-atmosphere system and the climate. We provide brief overviews of the development of some applications, including the feasibility of generating Climate Data Records. We summarize the important role of the Group for High Resolution SST (GHRSST) in providing a forum for scientists and operational practitioners to discuss problems and results, and to help coordinate activities world-wide, including alignment of data formatting and protocols and research. The challenges of burgeoning data volumes, data distribution and analysis have benefited from simultaneous progress in computing power, high capacity storage, and communications over the Internet, so we summarize the development and current capabilities of data archives. We conclude with an outlook of developments anticipated in the next decade or so.

Consistent Calibration of VIRR Reflective Solar Channels Onboard FY-3A, FY-3B, and FY-3C Using a Multisite Calibration Method

The FengYun-3 (FY-3) Visible Infrared Radiometer (VIRR), along with its predecessor, the Multispectral Visible Infrared Scanning Radiometer (MVISR), onboard the FY-1C and FY-1D, has collected continuous daily global observations for 18 years. Achieving accurate and consistent calibration for VIRR reflective solar bands (RSBs) has been challenging, as there is no onboard calibrator and the frequency of in situ vicarious calibration is limited. In this study, a new set of reflectance calibration coefficients were derived for RSBs of the FY-3A, FY-3B, and FY-3C VIRRs using a multisite (MST) calibration method. This method is an extension of a previous MST calibration method, which relies on radiative transfer modeling over the multiple stable earth sites, and no synchronous in situ measurements are needed; hence, it can be used to update the VIRR calibration on a daily basis. The on-orbit radiometric changes of the VIRR onboard the FY-3 series were assessed based on analyses of new sets of calibration slopes. Then, all recalibrated VIRR reflectance data over Libya 4, the most frequently used stable Earth site, were compared with those provided from the Level 1B (L1B) product. Additional validation was performed by comparing the recalibrated VIRR data with those derived from radiative transfer simulations using measurements from automatic calibration instruments in Dunhuang. The results indicate that the radiometric response changes of the VIRRs onboard FY-3A and FY-3B were larger than those of FY-3C VIRR and were wavelength dependent. The current approach can provide consistent VIRR reflectances across different FY-3 satellite platforms. After recalibration, differences in top-of-atmosphere (TOA) reflectance data across different VIRRs during the whole lifetime decreased from 5–10% to less than 3%. The comparison with the automatic calibration method indicates that MST calibration shows good accuracy and lower temporal oscillations.

Evaluation of sea surface temperature from FY-3C data

ABSTRACTThe daily sea surface temperatures (SSTs) derived from the visible and infrared scanning radiometer (VIRR) and microwave radiation imager (MWRI) aboard the Fengyun-3C (FY-3C) satellite are evaluated against the measurements of in-situ SST and Reynolds optimum interpolation daily 0.25° SST (OISST) products. Statistical results for 2015 reveal a mean bias ± standard deviation of error () for the daytime VIRR SST, night-time VIRR SST, daytime MWRI SST (MWRID), and night-time MWRI SST (MWRIN) of 0.5877 ± 1.3279°C, −0.4801 ± 1.2588°C, 0.6044 ± 3.9064°C, and 0.7653 ± 3.7307°C, respectively. According to the SST bias performance of each product for different periods and latitudes, it is clear that the SST biases of the VIRR products are the largest at low latitudes and are relatively lower at mid-high latitudes and that negative SST biases in the VIRR increase with varying time. Large abnormal SST biases from MWRI products occur in Time III (the 211th to 319th day of 2015), and the average values of the SST biases are 3.6010°C and 3.7822°C for the MWRID and MWRIN, respectively. We expect that our validation results for VIRR and MWRI products can help algorithm developers further enhance the accuracy of SST retrievals while also helping sensor designers improve the performance of sensors for the next generation of FY satellites.

Evaluation of Sea Surface Temperature From FY-3C VIRR Data in the Arctic

Daily 5-km sea surface temperature (SST) data from the Visible and Infrared Scanning Radiometer (VIRR) onboard the Fengyun-3C (FY-3C) satellite are evaluated for latitudes greater than 60° N against in situ and daily 4-km SST data from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite. Approximately five months of data are used for the evaluation, during August to December 2014. The in situ and 4-km MODIS SST data are averaged and resampled at a spatial resolution of 5 km, which is similar to that of the VIRR SST data. The bias and standard deviation of the SST difference between VIRR and buoy data are −0.12 °C and 0.93 °C, respectively. A three-way error analysis is conducted between VIRR, MODIS, and buoy SSTs to obtain standard deviations of error for each kind of observation. The separated standard deviations of the error are found to be 0.91 °C for the VIRR SST, 0.20 °C for the in situ SST, and 0.51 °C for the MODIS SST. The error sources are discussed. The results indicate that the FY-3C/VIRR SST product needs to be improved.

Assessment and Correction of on-Orbit Radiometric Calibration for FY-3 VIRR Thermal Infrared Channels

FengYun-3 (FY-3) Visible Infrared Radiometer (VIRR), along with its predecessor, Multispectral Visible Infrared Scanning Radiometer (MVISR), onboard FY-1C&D have had continuous global observation more than 14 years. This data record is valuable for weather prediction, climate monitoring, and environment research. Data quality is vital for satellite data assimilations in Numerical Weather Prediction (NWP) and quantitative remote sensing applications. In this paper, the accuracies of radiometric calibration for VIRR onboard FY-3A and FY-3B, in thermal infrared (TIR) channels, are evaluated using the Low Earth Orbit (LEO)-LEO simultaneous nadir overpass intercalibration method. Hyperspectral and high-quality observations from Infrared Atmosphere Sounding Instrument (IASI) onboard METOP-A are used as reference. The biases of VIRR measurements with respect to IASI over one-and-a-half years indicate that the TIR calibration accuracy of FY-3B VIRR is better than that of FY-3A VIRR. The brightness temperature (BT) measured by FY-3A/VIRR is cooler than that measured by IASI with monthly mean biases ranging from −2 K to −1 K for channel 4 and −1 K to 0.2 K for channel 5. Measurements from FY-3B/VIRR are more consistent with that from IASI, and the annual mean biases are 0.84 ± 0.16 K and −0.66 ± 0.18 K for channels 4 and 5, respectively. The BT biases of FY-3A/VIRR show scene temperature-dependence and seasonal variation, which are not found from FY-3B/VIRR BT biases. The temperature-dependent biases are shown to be attributed to the nonlinearity of detectors. New nonlinear correction coefficients of FY-3A/VIRR TIR channels are reevaluated using various collocation samples. Verification results indicate that the use of the new nonlinear correction can greatly correct the scene temperature-dependent and systematic biases.

Characterization of CRCS Dunhuang test site and vicarious calibration utilization for Fengyun (FY) series sensors

The Dunhuang test site, one of the China Radiometric Calibration Sites (CRCS) for the vicarious calibration (VC) of Chinese spaceborne sensors, was selected in 2008 by the Working Group on Calibration and Validation (WGCV) of the Committee on Earth Observation Satellites (CEOS) as one of the instrumented reference sites. The site is spatially uniform with a coefficient of variation (CV) (standard deviation / mean) less than 2% of spectral reflectance over the 10 km × 10 km central region, based on the imagery of the Medium Resolution Spectral Imager (MERSI) onboard the Fengyun 3A (FY-3A) satellite. This result is also proven by several ground truth measurements. The surface spectral reflectance is temporally stable with a CV of about 3% from 7-year Moderate Resolution Imaging Spectroradiometer (MODIS) surface albedo product and has been validated using the ground-based measurement eight times in 10 years. Several calibration/validation (Cal/Val) field campaigns for the site evaluation and VC have been conducted since 1999, and a database including atmospheric and surface characteristics has been established. The aerosol optical depth (AOD) at the Dunhuang site is low (τ550 is about 0.2), except for the dusty spring season from March to May. The surface reflectance of this site is about 15%–30% from the visible to near-infrared spectral region. The site surface is not Lambertian, with clearly direction-dependent reflectance variation especially at the large solar or observation zenith angles. The CRCS VC was the baseline operational calibration approach from 2002 for the Multichannel Visible and Infrared Scanning Radiometer (MVISR) onboard the FY-1C and FY-1D satellites. The approach is inherited by the optical imaging sensors (Visible and Infrared Radiometer (VIRR) and MERSI) of the Chinese second-generation polar-orbiting satellite FY-3A. The CRCS VC is used not only to correct the significant bias of preflight calibration in some bands of these sensors but also to monitor the sensor radiometric degradation. The Dunhuang site can also be used as the earth target in the cross-calibration for the FY satellite sensors.

Infrared thermography: An optical method in heat transfer and fluid flow visualisation

This paper deals with the evolution of infrared thermography into a powerful optical method to measure wall convective heat fluxes as well as to investigate the surface flow field behaviour over complex geometries. The most common heat-flux sensors, which are normally used for the measurements of convective heat transfer coefficients, are critically reviewed. Since the infrared scanning radiometer leads to the detection of numerous surface temperatures, its use allows taking into account the effects due to tangential conduction along the sensor; different operating methods together with their implementations are discussed. Finally, the capability of infrared thermography to deal with three complex fluid flow configurations is analysed.

A new method for cross-calibration of two satellite sensors

Given that many operational satellite sensors are not calibrated, while a handful of research sensors are, cross-calibration between the two types of sensor is a cost-effective means of calibration. A new method of sensor cross-calibration is demonstrated here using the Chinese Multi-channel Visible Infrared Scanning radiometer (MVIRS) and the US Moderate Resolution Imaging Spectrometer (MODIS). MVIRS has six channels, equivalent to the current National Oceanic and Atmospheric Administration's (NOAA) Advanced Very High Resolution Radiometer (AVHRR) and four additional ones for remote sensing of ocean colour and moisture. The MVIRS on-board China's polar-orbiting meteorological satellite (FY-1D) was launched on 15 May 2002 with an earlier overpass time than Terra. The sensor has no on-board calibration assembly. This study attempts to calibrate MVIRS against the well-calibrated MODIS, by taking a series of measures to account for their differences. Clear-sky measurements made from the two sensors in July-October 2002 were first collocated. Using the 6S radiative transfer model, MODIS reflectances measured at the top-of-the atmosphere were converted into surface reflectances. They were corrected to the viewing geometry of the MVIRS using the bidirectional reflectance distribution function (BRDF) measured on the ground. The spectral response functions of the two sensors were employed to account for spectral discrepancies. After these corrections, very close linear correlations were found between radiances estimated from the MODIS and the digital readings from the MVIRS, from which the calibration gains were derived. The gains differ considerably from the pre-launch values and are subject to degradation over time. The calibration accuracy is estimated to be less than 5%, which is compatible to that obtained by the more expensive vicarious calibration approach.

Thermo-fluid-dynamics of a complex fluid flow

The main purpose of the present work is to find connections between turbulent statistics of a jet in cross-flow and the convective heat transfer over the wall the jet issues from. The velocity field and the flow statistics are evaluated by means of the Particle Image Velocimetry (PIV) technique. The heated-thin-foil technique associated to the detection of temperature by means of an infrared scanning radiometer is used to perform convective heat transfer measurements. The study is restricted to jet to free stream velocity ratios ranging from 1 to 5 and to a Reynolds number equal to 8000. The vortical structures originating from the interaction of the jet with the cross-flow are visualized and the mean and instantaneous velocities are measured in the jet symmetry plane and in planes normal to the jet axis. For most velocity ratios, a linkage appears to be found between the heat transfer and the in-plane turbulent kinetic energy measured close to the wall. Furthermore, the counter rotating vortex pair, which is bound to the lee surface of the jet, has a shape which is strongly dependent on the velocity ratio; this parameter has a strong influence also on the heat transfer in the vicinity of the jet exit section.

Real time seam tracking system for automated fusion arc welding

The demand for a simple and inexpensive yet flexible real time seam tracking system for automated fusion arc welding processes is ever increasing. To date, few techniques have been implemented in industry on a commercial basis, employing mostly thermovision devices, e.g. infrared vision cameras, infrared scanning radiometers, etc. or laser illuminated seam tracking systems. From the literature it appears that the use of simple vision sensors such as charge coupled device (CCD) cameras, which can monitor the surface temperature gradients as well as seam tracking operation in real time economically and reliably, has not yet been fully explored. It is thus conceived that further work is required in investigating real time seam tracking and adaptive control using image processing techniques and CCD cameras as they are inexpensive and robust as well as being sufficiently flexible. This highlights the importance of the present work, in which an attempt is made to extract geometrical parameters of the welding arc and to locate the weld seam ahead of the welding torch using images sensed by a simple CCD monochrome camera. The developed system has been tested successfully for fusion arc welding of butt joints with arc offsets, which are induced intentionally during experimentation.

Convective heat transfer and infrared thermography.

Infrared (IR) thermography, because of its two-dimensional and non-intrusive nature, can be exploited in industrial applications as well as in research. This paper deals with measurement of convective heat transfer coefficients (h) in three complex fluid flow configurations that concern the main aspects of both internal and external cooling of turbine engine components: (1) flow in ribbed, or smooth, channels connected by a 180 degrees sharp turn, (2) a jet in cross-flow, and (3) a jet impinging on a wall. The aim of this study was to acquire detailed measurements of h distribution in complex flow configurations related to both internal and external cooling of turbine components. The heated thin foil technique, which involves the detection of surface temperature by means of an IR scanning radiometer, was exploited to measure h. Particle image velocimetry was also used in one of the configurations to precisely determine the velocity field.

Thermographic investigation of some surface flow patterns

Infrared (IR) thermography, due to its two-dimensionality and non-contact character, can be usefully employed in a vast variety of heat transfer industrial applications as well as research fields. The present work deals with measurements of temperature and/or convective heat transfer coefficients in several types of fluid flow configurations studied by means of the IR scanning radiometer applied to the heated-thin-foil technique. In more details, it is analysed the capability of the infrared system to study particular phenomena such as: the heat transfer, including the spiral vortical structures developing at transition, over a disk rotating in still air; the thermal exchange enhancement induced by a jet centrally impinging on the rotating disk; the complex heat transfer pattern associated with a jet in cross-flow.

Heat Transfer Measurements on a Rotating Disk

Heat transfer to a rotating disk is measured for a wide range of Reynolds number values in the laminar, transitional and turbulent flow regimes. Measurements are performed by making use of the heated‐thin‐foil technique and by gauging temperature maps with an infrared scanning radiometer. The use of the IR radiometer is advantageous on account of its relatively good spatial resolution and thermal sensitivity and because it allows one to perform measurements down to very low local Reynolds numbers. Data is obtained on three disks, having an external diameter varying from 150mm to 450mm; the smallest disk is used only to measure the adiabatic wall temperature and can rotate up to 21,O00rpm. Heat transfer results are presented in terms of Nusselt and Reynolds numbers based on the local radius and show a substantial agreement with previous experimental and theoretical analyses. Transition to turbulent flow is found at about Re = 250, 000. A discussion about the role played by the adiabatic wall temperature is also included.

Influence of shear layer dynamics on impingement heat transfer

Measurements of convective heat transfer coefficients on a flat plate with an air jet impinging on it perpendicularly are made to investigate the influence of some governing parameters. Particular attention is focused on the effects of the shear layer dynamics. For certain flow conditions and/or test arrangements, coherent structures and/or recirculation currents are observed affecting the distribution of the heat transfer coefficients. Measurements of wall temperature as well as of adiabatic wall temperature of the stream are made by means of an infrared scanning radiometer, and the heat transfer coefficients are calculated by means of the so-called heated thin foil technique. The data are reduced in dimensionless form as Nusselt numbers and compared with data from the available literature. Both spatial distributions and averaged values of the Nusselt number are discussed. A new explanation for the second peak in the local Nusselt number is proposed.

Azimuthal instability in an impinging jet: adiabatic wall temperature distribution

The present work has been aimed at gaining some new insights into instability phenomena arising when an air jet impinges on a flat plate under certain conditions. At a critical Mach number, depending on the impingement distance, the jet loses its circumferential appearance with the formation of evenly equidistant azimuthal structures, whose number and location depend on the nozzle geometry and on the flow conditions. The instability is investigated in terms of pressure and adiabatic wall temperature; the latter is measured by means of an infrared scanning radiometer. Entrainment effects are found to play a key role in the priming and evolution of the instability.

Quantitative heat transfer measurements in hypersonic wind tunnels by means of infrared thermography

A description of infrared (IR) thermography, as it is employed in a hypersonic blowdown wind tunnel for the acquisition of high quality two-dimensional heat transfer data over aerodynamic surfaces, is given. It is shown that the availability of an IR scanning radiometer and a standard digital image processing (DIP) system in the laboratory provides the means for highly efficient (in terms of time and cost) heat transfer measurement, with accuracy levels comparable to those achieved by classical discrete point gauges, such as thin-film surface resistance thermometers and thermocouples. The advantages of IR thermal mapping over the classical techniques, not only in measuring heat transfer distributions over complex three-dimensional configurations and in locating and quantifying highly localized hot spots, but also in interpreting puzzling results observed on simple configurations, are illustrated using a series of examples. A discussion of the limitations of the technique indicates that most of such limitations are common to classical 'zero-dimensional' instrumentation as well. >