All‐sky assimilation of infrared (IR) radiances has been developed for water vapor bands of the geostationary satellite Himawari‐8 in the operational global data assimilation system. Cloud‐dependent ...quality control, bias correction, and observation error modeling are essential developments to effectively utilize the all‐sky radiances (ASRs). ASR assimilation increases the assimilated number of observations by 2.8 times and improves the coverage relative to the traditional clear‐sky radiance (CSR) assimilation. The additional observations better alleviate model dry biases in the middle and upper tropospheric humidity. ASR assimilation brings statistically significant improvements in the background (first guess) in humidity, temperature, and wind over the CSR assimilation. It also better improves short‐range forecasts of the middle and upper tropospheric temperature and humidity up to day 3 in the Tropics. A mixed impact in the stratospheric temperature is under investigation. The impacts of various aspects of the ASR assimilation configuration are evaluated with sensitivity assimilation experiments. The interband correlation and cloud‐dependent standard deviation of the observation error are crucial, whereas the cloud dependency of the correlation is not so important. Although ASRs at a single band were assimilated in many previous studies targeting severe weather using research‐based regional assimilation systems due to decreasing independent information in the presence of clouds, they are distinctly inferior to not only ASRs at multiple bands but also CSRs at multiple bands in a global data assimilation system that contains fewer cloud‐affected scenes. The cloud‐dependent bias correction predictors are essential in the presence of observation‐minus‐background bias that increases with cloud effects.
All‐sky assimilation of infrared radiances has been developed for water vapor bands of the geostationary satellite of Himawari‐8 in the operational global data assimilation system. All‐sky radiance (ASR) assimilation increases the assimilated number of observations by 2.8 times and improves the coverage than the traditional clear‐sky radiance (CSR) assimilation. It better alleviates dry biases in the middle and upper tropospheric humidity and significantly improves short‐range forecasts of humidity and temperature in the Tropics.
In this study, a method for assimilating FY4A advanced geostationary radiance imager (AGRI) cirrus‐effected radiances (CER) is investigated, and the impact of this method on water vapor analysis and ...rainstorm forecasting is examined through observing system simulation experiments and actual case experiments. The high proportion of inverted humidity profiles in the cirrus‐effected pixels is the main reason for the negative effect of assimilation in the mid‐to‐lower troposphere. To address this, relevant constraint conditions are incorporated into the cost function. The statistical results reveal that the addition of a CER assimilation improves the analysis increment of water vapor, with pattern correlation coefficients of 0.33, 0.35, and 0.20 at 200, 300, and 400 hPa, respectively, which are greater than those of a clear‐sky radiance assimilation (0.28, 0.33, and 0.17, respectively). Moreover, the inclusion of a CER assimilation greatly improves data utilization, and has a neutral to positive effect on precipitation forecasting.
Plain Language Summary
Infrared all‐sky radiance assimilation is an attractive but challenging problem in satellite data assimilation. Is there an alternative approach to achieve the assimilation of infrared radiance for a certain type of cloud? It is found that cirrus clouds, which are loose ice clouds composed of ice crystals, can partially transmit infrared radiance and are large in number. Considering these advantages, a new direct assimilation method for FY4A advanced geostationary radiance imager (AGRI) cirrus‐effected radiances is proposed in this paper. The method addresses the uncertainty in the assimilation of cirrus‐effected radiances by adding weak constraints of inverse humidity. This research highlights the substantial increase in AGRI data usage when incorporating cirrus‐effected radiance data, as well as the neutral‐to‐positive impact on water vapor analysis and precipitation forecasting. This study also suggests that future endeavors could combine infrared channels with lower‐level microwave channels, which may have a more significant contribution to infrared radiance assimilation.
Key Points
A high percentage of inverse humidity exists in the atmospheric profile corresponding to cirrus cloud fields of view over land
The assimilation of cirrus cloud pixels greatly improves the utilization rate
Assimilating advanced geostationary radiance imager cirrus‐effected radiances has a neutral to positive effect on water vapor analysis and precipitation forecasting
This study examines the advantages of infrared all‐sky radiance (ASR) assimilation over traditional clear‐sky radiance (CSR) assimilation using a mesoscale LETKF data assimilation system. To ...effectively assimilate ASR data from the Himawari‐8 geostationary satellite, a cloud‐dependent quality‐control procedure and an observation error model were developed. A single humidity band to be assimilated and thinning distance were determined based on observation error statistics. The operational pre‐processing and parameter settings, such as observation errors and an adaptive bias correction for CSR, were incorporated into the LETKF data assimilation system.
A comparison of the impacts of assimilating ASRs and CSRs was accomplished using single‐cycle and 10‐day cycle assimilation experiments. Study results revealed that ASR assimilation provided a higher degree of improvement in the first‐guess fit for conventional observations and satellite retrievals with respect to temperature, moisture and wind. Furthermore, ASR assimilation displayed a more stable improvement in the prediction of a severe rainfall event because it has more universal data coverage than CSR. Adaptive bias correction schemes with two different sets of predictors for ASRs were tested and revealed the difficulty in extracting additional information for the assimilation of no‐bias corrected ASR due to complicated bias factors. This was in contrast to the CSR assimilation, where bias correction had a positive impact.
Assimilating infrared all‐sky radiances (ASRs) at a humidity band from Himawari‐8 has been developed in a regional mesoscale data assimilation system and its impacts were carefully investigated in comparison with clear‐sky radiance (CSR) assimilation. The figure shows that ASR assimilation provides a more stable improvement in the prediction of severe rainfall at different initial conditions because it has more universal data coverage than CSR assimilation.
Three‐hour accumulated rainfall and surface pressure forecasts valid at 0000 UTC 10 September 2015, initialised at (a–c) 1200 UTC 8 September, (d–f) 0000 UTC 9 September, for (a,d) CNTL, (b,e) ASREXP, and (c,f) CSREXP. (g) 3 h accumulated rainfall observations of RAP and surface pressure from the operational meso‐analysis at 0000 UTC 10 September.
Satellite images are occasionally limited in some applications because of their specified imaging time and observation angles, and it is one solution to simulate them with radiative transfer models, ...which can reduce these limitations. However, there are many numerical differences between the simulated images and the satellite images. In order to calibrate simulated radiance, the discrete anisotropic radiative transfer (DART) model is used to simulate the red, green, and blue band images corresponding to the Sentinel-2 images, and an iterative algorithm, which is based on the assumption that the pixel radiance is the cumulation of all the elements radiance within the scene, is proposed to minimize discrepancies between the simulated images and satellite images. The results show that: 1) the algorithm is effective to enhance the similarity of the simulated images and Sentinel-2 images. There are differences in the red, green, and blue bands of 0.70 W<inline-formula> <tex-math notation="LaTeX">\cdot </tex-math></inline-formula> mt<inline-formula> <tex-math notation="LaTeX">^{-2}\cdot {\mathrm { m}}^{-1}\cdot {\mathrm { sr}}^{-1} </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">1.73~{\mathrm { W}}\cdot {\mathrm { m}}^{-2}\cdot {\mathrm { m}}^{-1}\cdot {\mathrm { sr}}^{-1} </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">- 1.57~{\mathrm { W}}\cdot {\mathrm { m}}^{-2}\cdot {\mathrm { m}}^{-1}\cdot {\mathrm { sr}}^{-1} </tex-math></inline-formula> between the calibrated images and Sentinel-2 images and the relative differences of 0.77%, 2.30%, and 2.33%, respectively. The radiance differences between the simulated images (before and after calibration) and satellite images decreased from 5.34-<inline-formula> <tex-math notation="LaTeX">77.78~{\mathrm { W}}\cdot {\mathrm { m}}^{-2}\cdot {\mathrm { m}}^{-1}\cdot {\mathrm { sr}}^{-1} </tex-math></inline-formula> to 0.01-<inline-formula> <tex-math notation="LaTeX">4.01~{\mathrm { W}}\cdot {\mathrm { m}}^{-2}\cdot {\mathrm { m}}^{-1}\cdot {\mathrm { sr}}^{-1} </tex-math></inline-formula>, and the correlation coefficient increased from 0.39-0.41 to 0.60-0.64 and 2) it is varied for the different ground elements' responses to the iteration algorithm; the simpler the ground element is, the better the results become. The methodology is useful to improve the precise of urban radiance simulation and is potential in minimizing errors in parameter estimation and expanding temporal analysis.
Clear‐sky radiances (CSRs) derived from observations made by imager sensors on board geostationary satellites are widely used in most operational numerical weather prediction systems. CSRs have data ...on tropospheric water vapour and temperatures, and the products at water vapour bands are generally assimilated into global data assimilation systems. In another band, known as the CO2 band (13.3–13.4 μm), CSRs are not used widely yet, despite having a wealth of information about temperatures in the mid‐ and low troposphere. This is mainly because of the high surface sensitivity of this band, which makes it difficult to accurately simulate brightness temperatures when there are non‐negligible errors in the surface parameters in the models. This article quantitatively investigated the surface sensitivities of CO2 and water vapour bands, which have the sensitivity under dry atmospheric conditions, and developed retrieval of land surface temperature (LST) from window band CSRs to obtain a more accurate simulated brightness temperature. Additionally, it was discovered that the retrieved LST outperformed that from the model in short‐range forecasts for the low‐water‐vapour band (7.3 μm) CSR data assimilation, and throughout the forecasting period, especially in the tropics, for the CO2 band CSR data assimilation. We also examined an unexpected improvement in the low troposphere in the model's LST trials, and we concluded that it was related to the relationship between the LST and atmospheric temperature biases.
Surface parameters' accuracy influences the radiative transfer calculation for surface‐sensitive radiance assimilation. We developed a method to retrieve land surface temperature (LST) from clear‐sky radiances (CSRs) at window band CSRs. The impact of CO2 band (13.3–13.4 μm) CSR assimilation with the retrieved LST was generally positive, whereas that with the model LST showed an intense diurnal cycle in the low troposphere. This was related to the diurnal variation of model biases of LST and atmospheric temperature.
The released VIIRS DNB nightly images, also known as VIIRS DNB daily nighttime images, provide rich information for time series analysis of global socioeconomic dynamics. Anisotropic characteristic ...is a possible factor that influences the VIIRS DNB radiance at night and its time series analysis. This study aims to investigate the relationship between viewing angles and VIIRS DNB radiance of Suomi NPP satellite in urban areas. First, twenty-nine points were selected globally to explore the angle variation of Suomi NPP satellite views at night. We found that the variation of the satellite viewing zenith angle (VZA) is consistent (e.g. between 0° and 70°) since the range of VZA is fixed depending on the sensor design, and the range of viewing azimuth angle (VAA) increases with the increase of latitude. Second, thirty points in cities of Beijing, Houston, Los Angeles, Moscow, Quito and Sydney, were used to investigate the angle-radiance relationship. We proposed a zenith-radiance quadratic (ZRQ) model and a zenith-azimuth-radiance binary quadratic (ZARBQ) model to quantify the relationship between satellite viewing angles and artificial light radiance, which has been corrected by removing the moonlight and atmospheric impact from VIIRS DNB radiance products. For all the thirty points, the ZRQ and ZARBQ analysis have averaged R2 of 0.50 and 0.53, respectively, which indicates that the viewing angles are important factors influencing the variation of the artificial light radiance, but extending zenith to zenith-azimuth does not much better explain the variation of the observed artificial light. Importantly, based on the data analysis, we can make the hypothesis that building height may affect the relationship between VZA and artificial light, and cold and hot spot effects are clearly found in tall building areas. These findings are potentially useful to reconstruct more stable time series VIIRS DNB images for socioeconomic applications by removing the angular effects.
•A workflow is developed to simulate multi-sectional facades with customized controls.•Combinations of roller shades and blinds as integrated façade systems are evaluated.•Multi-sectional facades ...controlled properly increase daylight near the rear wall.•Controlling diffuse shades and blinds in the top section reduces glare.•Using the same shading material for different locations might cause discomfort glare.
Daylighting plays an important role in building design. To maintain visual comfort and provide outdoor views, designers can use multi-sectional facades to extend daylit areas by daylight-redirecting devices and minimize undesired sunlight by movable shading devices. Beyond using specially designed light-redirecting systems, a combination of common shading devices – roller shades and blinds – may be used to meet aesthetic and cost requirements. However, the evaluation and simulation of multi-sectional facades are challenging, especially when the modeling involves complex fenestration systems and automated control strategies. In this study, we evaluate the effectiveness of multi-sectional facades with a roller shade and blind combination. Two control strategies are designed for two different multi-sectional facades, with a workflow developed for the evaluation. This workflow applies Radiance’s three-phase method for each shading state to model movable shades. External scripts are adopted to describe control algorithms and to generate annual results and daylight metrics. The workflow facilitates simulations of daylighting conditions for spaces equipped with both movable shading devices and daylight-redirecting devices under any customized control algorithms. The results demonstrate that the combinations of roller shades, blinds, and proper control algorithms greatly increase daylight near a rear wall compared to cases with only controlled roller shades, and do not cause glare. The combination with fixed blinds and controlled roller shades at the top section and another controlled roller shade at the middle section works well for rear spaces with south-facing or west-facing facades in both Taipei and New York.
Quantum yield and brightness Wong, Ka-Leung; Bünzli, Jean-Claude G.; Tanner, Peter A.
Journal of luminescence,
August 2020, 2020-08-00, Letnik:
224
Journal Article
Recenzirano
Brightness has different meaning in different contexts and some of these are reviewed. The scientific definition of brightness does not represent our perception. The current definition is that from ...the IUPAC Gold Book and is mainly restricted to solutions. We propose a definition for solids that requires the use of an integrating sphere. Terms related to quantum yield and efficiency are clarified as well as those characterizing light properties.
•Different perceptions of brightness noted.•Clear definitions given for quantum yield and brightness.•Terms related to quantum yield and efficiency are clarified.
Neural Radiance Fields (NeRFs) have recently emerged as a powerful paradigm for the representation of natural, complex 3D scenes. Neural Radiance Fields (NeRFs) represent continuous volumetric ...density and RGB values in a neural network, and generate photo-realistic images from unseen camera viewpoints through ray tracing. We propose an algorithm for navigating a robot through a 3D environment represented as a NeRF using only an onboard RGB camera for localization. We assume the NeRF for the scene has been pre-trained offline, and the robot's objective is to navigate through unoccupied space in the NeRF to reach a goal pose. We introduce a trajectory optimization algorithm that avoids collisions with high-density regions in the NeRF based on a discrete time version of differential flatness that is amenable to constraining the robot's full pose and control inputs. We also introduce an optimization based filtering method to estimate 6DoF pose and velocities for the robot in the NeRF given only an onboard RGB camera. We combine the trajectory planner with the pose filter in an online replanning loop to give a vision-based robot navigation pipeline. We present simulation results with a quadrotor robot navigating through a jungle gym environment, the inside of a church, and Stonehenge using only an RGB camera. We also demonstrate an omnidirectional ground robot navigating through the church, requiring it to reorient to fit through a narrow gap.
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