Narrow-band Model Research Articles

Effects of cross-sectional shape on the low observability of double serpentine nozzles

When unmanned combat aerial vehicles (UCAVs) egress from the battlefield after attacking the target, the defensive radar systems detect signals reflected by the cavity structure of the nozzle and engine of the UCAVs, threatening their survivability. Infrared (IR) guided missiles can also threaten them by detecting the gaseous plume and hot engine parts. We present a comprehensive investigation of the effects of the cross-sectional shape of double serpentine nozzles on thrust, IR signature, and radar cross section (RCS), which are associated with propulsive performance and low observability. The fillet radius and cross-sectional shape of the nozzles were considered as the main design variables. The thermal flow field was analyzed using the compressible Navier-Stokes equations, while the IR signature was analyzed with the radiative heat transfer equation with a narrow band model. The RCS was calculated using a multi-level fast multipole method of full Maxwell's equations instead of the approximate methods often employed. The double serpentine (DS) nozzle with an elliptical cross-section showed high pressure recovery and a 9.66 % lower IR signature than the DS nozzle with a rectangular cross section. The maximum RCS and mean RCS were lowest for the DS nozzle with an elliptical cross section, with a maximum difference in maximum RCS of 383 % and mean RCS of 90 % compared with the DS nozzle with a rectangular cross section. The DS nozzle with an elliptical cross section distributes the current more evenly across the central part of the engine than the DS nozzle with a rectangular cross section. The DS nozzle with an elliptical cross-section showed excellent nozzle performance with a negligible difference in thrust. In addition, the results show that the cross-sectional shape of the nozzles has different levels of impact on thrust and pressure recovery (negligible), IR signature (limited), and RCS (significant).

The influence of radiation modeling on flame characteristics and emissions prediction in microcombustors with Ammonia/Hydrogen blends

This study advances numerical methodologies for designing microcombustor-based thermophotovoltaic systems by incorporating comprehensive analyses of radiation models and absorption coefficients. It examines the impact of non-premixed hydrogen-ammonia-air fuel blends on the micro combustion process using three-dimensional CFD simulations on a Y-shaped microcombustor under atmospheric conditions.Key to this research is modeling radiative heat transfer from multiple species, including ammonia (NH3), nitric oxide (NO), and water vapor, ensuring accurate predictions and optimization of thermal behavior and efficiency. Three modeling approaches were compared: a multispecies Planck-mean approximation radiation model (PMAC), a narrowband model for water vapor, and a scenario excluding radiation effects.The PMAC model, incorporating the absorption coefficients of ammonia and its products, consistently produced lower errors in flame length compared to the NB method across all equivalence ratios, with errors ranging from 0 % to 7 % for PMAC and 10 % to 30 % for NB, with the lowest error observed at Φ = 1.0. Additionally, the prediction of laminar burning velocity (LBV) differed by approximately 4 % between the two models.Considering different fuel blends, two scenarios were compared: constant input thermal power and constant fuel flow rate. Efficiency in the constant input thermal power scenario maintained higher radiation efficiency, in the range of 32–38%. Additionally, radiation efficiency initially increased with increasing H2 content but subsequently decreased for high H2 values due to effects on flame area, flame position, and temperature.

SBS suppression in fiber amplifiers with a broadband seed

We present a scalar, time-dependent, plane-wave model for stimulated Brillouin scattering (SBS) within a fiber amplifier having a seed linewidth comparable to, or greater than, the Brillouin frequency shift. The broadband model introduces the existence of a backward anti-Stokes wave, in addition to the Stokes wave present in the narrowband model. The model also incorporates a Fresnel reflection within the fiber or at the exit face. In the absence of Fresnel reflections, the SBS threshold increases linearly with seed linewidth, up to linewidths of at least three times the Brillouin frequency shift. In the presence of Fresnel reflections that seed the Stokes wave, the threshold increases sub-linearly, which agrees with previously reported experimental results. For non-zero reflections and modulation formats with very compact spectra, the threshold can decrease with bandwidth in the region 16–24 GHz due to seeding of the Stokes wave.

Practical approaches for evaluating radiative heat from high pressure hydrogen flame

As the construction of hydrogen stations and other hydrogen-related facilities progresses, it becomes increasingly crucial for safety designs to account for scenarios where leaked hydrogen might ignite. Since a hydrogen flame is usually invisible, detection must rely on radiative heat or temperature. While it is possible to predict accurate radiative heat flux from a high pressure hydrogen jet flame through detailed numerical calculations of hydrogen combustion with its radiation, the objective of this study is to provide a simpler and more accurate prediction method. Previous experimental data of radiative heat flux, Qr from high pressure hydrogen jet flames were compiled, and a simple experimental equation Qr=1463.3(Lo/Lf)−2.32 was derived, where Lf and Lo represent the flame length and the distance perpendicular to the flame axis from the midpoint of the flame length to the observer, respectively. Radiative heat fluxes were computed through detailed numerical simulations using three types of water vapor radiation models: Goody's narrow random band model, the exponential broad band model by Edward and Elsasser's narrow regular band model. The temperature and water vapor partial pressure distributions obtained from numerical simulations were used as input conditions. The results were found to be in good agreement with the experimental equation. Moreover, a simple diagram representing the radiative heat flux from a hydrogen flame was derived using the method of cylinder-like approximation. The results of this study show that if the hydrogen pressure and leakage aperture diameter are given, the radiative heat flux at a certain distance can be predicted with high accuracy. Additionally, the average value of emissivity for the hydrogen diffusion flame was found to be on the order of 0.03.

Statistical Narrow Band model for vibrational nonequilibrium [formula omitted] radiation

This paper presents the development of a Statistical Narrow Band (SNB) model for CO2 in a nonequilibrium vibrational state. The population densities of the energy levels are modeled by a three-temperature approach (T,T12,T3) associated resp. to translation–rotation modes, symmetric-stretching and bending modes, and antisymmetric stretching mode, to compute nonequilibrium line by line (LBL) spectra. The nonequilibrium between vibrational temperatures induces spectral correlation issues between ησ/κσ and κσ, where ησ and κσ are the emission and absorption coefficients respectively. To overcome this issue, a vibrational splitting of the spectroscopic database is made to separate lines with completely different vibrational transitions. The SNB parameters are obtained by fitting the curves of growth from the LBL approach by a least squares error minimization using a Newton method for pure Lorentz and Doppler broadening regimes for each line class. The total SNB transmissivity is obtained by computing the product of each line class transmissivity, and the decorrelation between the spectra of the different classes is checked. Finally, the model is tested in Voigt broadening regime using a mixing rule by computing outlet radiative intensity of uniform and non-uniform columns and agrees well with the LBL approach. SNB parameters are available under request to the corresponding author.

Integrated modeling and coupling characteristics analysis of helicopter/engine/infrared suppressor

Abstract In order to explore the influence of the infrared stealth technology on the performance of the integrated helicopter/engine system, an integrated modeling method of helicopter/engine/infrared suppressor is proposed. Firstly, based on the power calculation model of the helicopter, combined with the high-precision turboshaft engine component-level model, an integrated simulation platform is built, which takes into account the nonlinear characteristics. Then, the aerodynamic characteristics of infrared suppressors under different engine operation states are studied by CFD numerical computation method, and the infrared radiation characteristics are obtained through combining the positive and negative ray tracing method and narrow band model method. Ultimately, the utilization of the power turbine outlet stagnation pressure is employed as the pivotal interface linking the turboshaft engine and the infrared suppressor in order to formulate an integrated model encompassing the helicopter, engine, and infrared suppressor subsystems. The simulation results demonstrate that compared with the conventional exhaust system, the application of the infrared suppressor greatly enhances the stealth performance of the helicopter, but also results in the unexpected decrease in engine output power. Moreover, the specific fuel consumption of the turboshaft engine increase and the compressor surge margin decreases in case of the consistent flight condition.

New coefficients of the weighted-sum-of-gray-gases model for gas radiation characteristics of hydrogen/natural gas blends combustion

To achieve carbon neutrality, hydrogen/natural gas blends are gaining momentum as a clean low-carbon fuel for the future. In order to accurately carry out the CFD numerical simulation of hydrogen/natural gas blends combustion, it is imperative to establish a precise model for gas radiation characteristics. The existing weighted-sum-of-gray-gases model (WSGGM) is not suitable for high hydrogen content fuels, such as hydrogen/natural gas blends. Hence, new coefficients of WSGGM is formulated specifically for the combustion of hydrogen/natural gas blends, drawing upon the groundwork established by the statistical narrow-band model (SNB model). This model is specifically designed to be applicable within the ambient pressures, encompassing the temperature regime of 400–2500 K, a path-length range of 0.001–60 m, and a hydrogen blending ratio of 20%–70%. The radiative heat transfer characteristics of the sum of the molar fraction of H2O and CO2 at 0.9, 0.6, and 0.3 were studied according to application conditions. The WSGGM is implemented to compute the radiative heat transfer in non-isothermal and non-homogeneous gas mixtures. When compared to the benchmark model, the deviation of the wall heat flux does not surpass 5.20%. The results demonstrate the excellent adaptability of the WSGG coefficients in simulating the radiative heat transfer during hydrogen/natural gas blends combustion.

Developing machine learning models for accurate prediction of radiative efficiency of greenhouse gases

BackgroundGreenhouse gases (GHGs), particularly halocarbons, contribute significantly to the radiative forcing of climate change due to their long lifetime. Accurate prediction of GHG radiative efficiency (RE) is required to assess the relative impacts of GHGs on climate change. MethodsAn RE dataset consisting of around 82 K molecules was generated using a narrow band model (NBM) and density functional theory (DFT) computed infrared spectra. This dataset, along with 568 experimentally available RE data, was utilized to develop machine learning (ML) models through a transfer learning approach. Significant findingsThe accuracy of REs calculated with NBM and DFT was evaluated against experimental data. A moderate level of agreement was observed, with a tendency to overestimate the results. ML models were then trained using DFT data, and their performance was compared using various model architectures. The directed message-passing neural network (DMPNN) model outperformed other models, and when combined with quantum mechanical features (ml-QM-DMPNN), a slight improvement was observed. The DMPNN and ml-QM-DMPNN models were refined by the transfer learning technique using the experimental dataset, which resulted in predicting experimental REs with root mean square errors (RMSEs) of 0.0582 and 0.0564 Wm−2ppb−1, respectively. This study offers critical insights into developing ML models that can predict REs of molecules, thereby facilitating the design of environmentally-friendly chemicals and materials.

High-Resolution Parameter Estimation for Wideband Radio Channel Sounding

Multidimensional channel sounding measures the geometrical structure of mobile radio propagation. The parameters of a multipath data model in terms of directions, time-of-flight and Doppler shift are estimated from observations in frequency, time and space. A maximum likelihood estimation framework allows joint high-resolution in all dimensions. The prerequisite for this is an appropriate parametric data model that represents the multipath propagation correctly. At the same time, a device data model is necessary that typically results from calibration measurements. The used model should be as simple as possible since its structure has a considerable effect on the estimation effort. For instance, the inherent effort in parameter search is reduced if the influence of the parameters is kept independent. Therefore, the data model is characterized by several approximations. The most important is the “narrowband assumption” which assumes a low relative bandwidth and also avoids considering any frequency response in magnitude and phase. We extend the well-known multidimensional RIMAX parameter estimation framework by including proper frequency responses. The advantage reveals itself with high bandwidth in the mmWave and sub-THz range. It allows for a more realistic modeling of antenna arrays, it breaks with the usual narrowband model and allows a better modeling of mutual coupling and time delay effects. If the interacting object extends over several delay bins (hence an extended target in radar terminology) we propose a model that assigns a short delay spread, respectively a frequency response to the propagation path that associates it to the respective object. We verify the validity of the device model by numerical experiments on simulated and measured antenna data and compare it to RIMAX. Additionally, we use synthetic data based on ray-tracing results and measurements both ranging from 27.0GHz to 33.0GHz with known ground truth information and show that the proposed estimator delivers better performance for higher relative bandwidths than the conventional RIMAX implementation.

A Wide-Band Modeling Research of Voltage Transformer in EMU

Considering that current voltage transformer models of electrical multiple units (EMUs) are narrow-band models or transformer models, this paper introduces a wide-band model of EMU voltage transformers based on the vector fitting method, circuit synthesis theory and black-box model theory. The admittances of voltage transformers from 30 kHz to 5 MHz are measured by the vector network analyzer, the branch admittances in the pi-type equivalent circuit are calculated according to the equation of a two-port network equivalent circuit. Based on the vector matching method, the rational function formulas of branch admittances are obtained, and the formulas are converted into the circuit models by circuit synthesis theory. The pi-type equivalent circuit model is constructed in the simulation software, and so is the voltage transformer model in the range of 30 kHz–5 MHz. The frequency sweeping method is used to measure the transmission characteristics from direct current (DC)to 30 kHz. The pi-type model is modified according to transmission characteristics, whereby the wide-band model in DC-5 MHz is obtained. Fast pulse experiments are carried out on the voltage transformer, and the actual injected fast pulse voltage is used as the excitation source in the simulation model. The measurement and simulation results on the secondary side of the voltage transformer show that the wide-band model has a high accuracy.

On the roles of humidification and radiation during the ignition of ammonia–hydrogen–air mixtures

It is well established that radiation plays an important role in the combustion process of premixed combustible mixtures, which significantly affects the flame temperature and chemical reaction rates during flame propagation. However, the impact of radiation, especially the radiation reabsorption effect, on minimum ignition energy (Emin) still lacks thorough research and understanding. In this study, the ignition processes of spherical NH3/H2/H2O/O2/N2 flames were simulated. Three different computational models, the adiabatic model (ADI), the optically thin model (OTM) and the statistical narrow-band model (SNB), were employed to determine the radiation effect (including both radiative heat loss and reabsorption) on Emin. Results indicated that the water content in the premixture suppressed ignition; characteristically, the addition of vol. 9.63% H2O in the premixture resulted in a nearly 40% increase of Emin under adiabatic condition. Both radiative heat loss and reabsorption effects increased Emin. The radiation effects on Emin, quantified as the relative differences between the OTM-/SNB- and ADI-obtained Emin, were up to 16.47% (for radiative heat loss) and 17.65% (for radiation reabsorption), respectively. It was further demonstrated that radiation increased Emin through the combination of three aspects: thermal effect, chemical effect and flame structure effect. The thermal effect, induced by the outward radiative emission, reduced the ignition kernel temperature significantly. The reduced temperature decelerated chemical reactions and then suppressed the chemical heat release, i.e., the chemical effect as reflected by the concentrations of H, O and OH radicals. Furthermore, the larger flame thickness obtained by the radiation models slowed down the diffusion of fuels, which weakened the chemical heat release and eventually increased the Emin. Moreover, the reaction-diffusion region simulated by SNB was enlarged due to the radiation reabsorption, and thus, Emin obtained by SNB was higher than that by OTM.

Measurement report: Radiative efficiencies of (CF3)2CFCN, CF3OCFCF2, and CF3OCF2CF3

Abstract. Absorption cross sections of emerging greenhouse gases (GHGs) were measured to estimate the radiative efficiency using high-resolution Fourier transform infrared spectroscopy (HR-FTIR). For quantitative spectroscopy, the Beer–Lambert parameters of absorber pressure, temperature, and optical path length (OPL) were accurately determined to be traceable to the primary standards. The OPL of the multipass cell mounted on the HR-FTIR spectrometer was spectroscopically calibrated. A ratio of the averaged N2O absorptions was found to be in the range of 2217.4–2219.0 cm−1, with a spectral resolution of 0.026 cm−1, yielding a ratio of OPLs between the multipass cell and reference cell. This cell-to-cell comparison method is free from the uncertainty of the referring line strength, which reduced the calibration uncertainty compared with the direct line-strength referring method. With the OPL-calibrated multipass cell (3.169 ± 0.079 m), the absorption cross sections were measured at low absorber pressures with a spectral resolution of 2 cm−1, integrated at 10 cm−1 intervals, and multiplied by the new narrow band model to yield the radiative efficiencies. The radiative efficiency values of CF4, SF6, and NF3 were evaluated to be 0.085 ± 0.002, 0.573 ± 0.016, and 0.195 ± 0.008 W m−2 ppb−1, respectively, which are consistent with previously reported values. For the emerging GHGs, the radiative efficiency values were determined to be 0.201 ± 0.008 W m−2 ppb−1 for heptafluoroisobutyronitrile (CF3)2CFCN; commercially referred to as Novec-4710), 0.328 ± 0.013 W m−2 ppb−1 for perfluoro methyl vinyl ether (CF3OCFCF2; PMVE), and 0.544 ± 0.022 W m−2 ppb−1 for 1,1,1,2,2-pentafluoro-2-(trifluoromethoxy)ethane (CF3OCF2CF3; PFMEE).

A new WSGG radiation model of CO/CO2 mixed gas for solar-driven coal/biomass fuel gasification

Gasification driven by solar energy with CO2 is an ideal way of low-carbon resource utilization. However, there is a lack of research on the radiation heat transfer process which is important in gasification simulation. In this study, we developed a new the weighted-sum-of-gray-gases (WSGG) model to calculate the radiation heat transfer properties of CO and CO2 mixtures in solar-driven coal/biomass fuel gasification. Benchmarked against the statistical narrow-band model (SNB) of the EM2C laboratory, the WSGG model is suitable for the temperature range of 400–2500 K and the path length range of 0.001–60 m. This study also explored the effect of the CO/CO2 molar ratio on the overall emissivity of the mixture. Furthermore, the model introduces a pressure term into the emissivity calculation process and broadens the pressure range (1 bar, 5 bar, 45 bar). For the first time, the WSGG model is applied to the case where the H/C element ratio is 0, and the fluctuating temperature distribution case (1000 – 2000 K) is analyzed, which is suitable for coal/biomass fuel gasification. In addition, this study calculated the one-dimensional radiation transfer equation. The results show that the average radiation source term difference between the new WSGG and the benchmark SNB model is within 5 % in common solar gasification engineering conditions (5 bar, 5 m). Meanwhile, this study also clarified the effect of pressure on the radiation heat transfer with different temperatures.

Entropy generation analysis of a three-dimensional coal-fired furnace: A realistic study

An analysis of the entropy generation by radiative heat transfer in a three-dimensional virtual coal-fired furnace is performed. The gases, including CO2 and H2O, and particles, including soot, unburnt char and ash, are considered as a participating medium. The radiative transfer equation for a non-grey medium was solved by the discrete ordinate method, in which the radiative properties of the gases, soot, unburnt char and ash were obtained by using the statistical narrow-band correlated-k model, Rayleigh's theory, and Mie theory, respectively. The distributions of the local volumetric rate of entropy generation and the local rate of entropy generation at the wall are calculated. The contributions of various media in coal-burning furnaces to the radiative entropy generation rate (REGR) are evaluated, and the effects of several important factors, such as the oxidizer atmosphere, burnout rate, and the volume fraction of soot, unburnt char and ash on the REGR and dimensionless entropy generation were also investigated. The numerical results show that the irreversibility of the particle radiation contributes more than 80% of the volumetric radiative entropy generation. The concentration of particles also has an important effect on REGR, which decreases by 41% when the concentration of unburnt char and ash increases from 10 ppm to 50 ppm and decreases by 70% when the concentration of soot increases from 1 ppm to 6 ppm in a real-size furnace such as an optically thick furnace.

A discrete spectral contributions based statistical narrow-band model for high-temperature combustion systems

In this work, we present a discrete spectral contribution based statistical narrow-band model (DSC-SNB) to solve the radiative transfer of high-temperature combustion systems, which employs a discrete spectral strategy to considerably improve the accuracy of the traditional SNB model. Based on the contribution of different gases to radiation, the DSC-SNB model divides the spectral lines into different groups within the spectral interval based on the low-level transition energies (E“). Treating the Line-by-Line (LBL) approach as the benchmark solution, several inhomogeneous high-temperature H2O-CO2-CO mixture columns are adopted to evaluate the DSC-SNB model. Results show that the DSC-SNB model performance is comparable with the traditional SNB model for isothermal gas mixture columns. The DSC-SNB model exhibits high accuracy under mid-high temperature or pure high temperature without low-temperature wrapping, outperforming the traditional SNB model. These findings could be used to reconstruct the multi-dimensional flame temperature field by building a highly accurate and efficient mathematical model for flame radiation prediction.

GPU-Accelerated infrared signature analysis model based on the Reverse Monte Carlo method

High-fidelity scene simulations are now possible thanks to advancements in computer technology. A fast analysis model for target infrared signature was developed by using the Graphics Processor Unit (GPU) device. The Malkmus statistical narrow band model is used to calculate the gas band-averaged transmittance. Mie scattering theory is used to calculate the particle scattering parameters, and based on the assumption that particles scatter light independently, the albedo and phase functions of the participating media are determined. The Reverse Monte Carlo method (RMCM) is used to complete the radiative transfer. Finally, a GPU device is used to accelerate the ray tracing process and achieve fast calculation of radiation. The calculation results show that the fast analysis model with high accuracy, and compared to Central Processing Unit (CPU) serial programs, the computational performance is greatly improved, with an acceleration ratio of more than 60. The thread block size has a significant impact on the occupancy and acceleration ratio, and the highest computational performance is obtained with the thread block size of 128. The scattering will reduce the acceleration ratio of the fast analysis model, and the performance will be reduced as the particle mass flow rate increases.

Numerical Study on Infrared Radiation Characteristics of Stealth Coating for Turbofan Engine Tail Nozzle

Infrared stealth technology plays a vital role in improving the survivability of future aircraft. The exhaust system is the main source of infrared radiation on the rear side of the aircraft, and stealth coating is an effective measure to reduce the infrared radiation on the solid wall of the nozzle. Mature commercial computational fluid dynamics software was used to obtain and analyze accurate data of the flow field to study the infrared radiation characteristics of the stealth coating on the turbofan engine nozzle. Furthermore, infrared simulation software based on the reverse Monte Carlo method, line-by-line calculation technique, and database technology for high-temperature gas parameters of a narrowband model were used to numerically simulate the exhaust system of a turbofan engine with infrared suppression coating. Assuming that the damage percentage of the external adjusting plate is constant, the findings reveal that the overall infrared radiation intensity exhibits a steadily increasing trend with the increase in the number of damaged adjusting plates. The maximum change in the infrared radiation intensity between eight damaged adjusting plates and one damaged adjusting plate was 11.67%. Thus, regular inspection and maintenance are required for the stealth coating on the external adjusting plate of the aero-engine tail nozzle to maintain stealth integrity.

Viscoelastic transcranial wave propagation modeling for neuronavigated focused ultrasound procedures in humans

Transcranial focused ultrasound (FUS) has gained significant attention as a non-invasive therapeutic technique that can reach both cortical and subcortical targets in the human brain. However, the skull barrier distorts the ultrasound beam and introduces significant losses that need to be accounted for. In this talk, I will present our efforts to develop high precise transcranial ultrasound modeling based on the open-source viscoelastic wave propagation solver BabelViscoFDTD and its application in neuronavigated procedures for FUS-based neuromodulation. The viscoelastic wave equation is expressed in isotropic stress tensors and displacement vectors, and their nodes are placed in a staggered grid arrangement. The solver uses a Cartesian O(4)-space O(2)-time FDTD scheme. A narrow-band quality factor models attenuation. A reduction of staircase artifacts can be enabled using a superposition operator. BabelViscoFDTD is optimized for multiple computing GPU and CPU backends (CUDA, OpenCL, Metal, and X86-64) and includes GPU-accelerated solvers of the Rayleigh-Sommerfeld equation and Bio-Heat thermal equations. We adapted the viscoelastic and thermal solvers to neuronavigate two FUS devices: A 128-element concaved array operable at 250 kHz and 700 kHz and a 4-ring concaved array operable at 500 kHz. The high degree of optimization of the solvers allow that numerical procedures (neuronavigation and modeling) can be performed in an Apple M1 Max (64 GB RAM) laptop computer.

Electromagnetic Based Communication Model for Dynamic Metasurface Antennas

Dynamic metasurface antennas (DMAs) arise as a promising technology in the field of massive multiple-input multiple-output (mMIMO) systems, offering the possibility of integrating a large number of antennas in a limited —and potentially large— aperture while keeping the required number of radio-frequency (RF) chains under control. Although envisioned as practical realizations of mMIMO systems, DMAs represent a new paradigm in the design of signal processing techniques (such as beamforming) due to the constraints inherent to their physical implementation, for which no complete models are available yet. In this work, we propose a complete and electromagnetic-compliant narrowband communication model for a generic DMA based system. Specifically, the model accounts for: i) the wave propagation and reflections throughout the waveguides that feed the antenna elements, ii) the mutual coupling both through the air and the waveguides, and iii) the insertion losses. Also, we integrate the electromagnetic model in the conventional digital communication model, providing a complete and useful framework to design and characterize the performance of these systems. Finally, the accuracy of the model is verified through full-wave simulations.

Water extraction from SAR images based on improved geodesic active contour.

The rapid and accurate acquisition of water body information is of great significance to water resource investigation, flood disaster monitoring, ecological environment protection, and other fields. In this paper, the water boundary is optimized and extracted from single-polarization SAR images based on an improved geodesic active contour model (IMGAC). Firstly, the rough extraction results of the water body were obtained according to the adaptive threshold, and then a narrowband model was established, and the signed pressure force (SPF) function was introduced into the geodesic active contour (GAC) model. Finally, the optimal water boundary was obtained through continuous iteration. Compared with the active contour (AC) model without edge and the traditional GAC model, the results show that the IMGAC model proposed in this paper can reduce the calculation efficiency and improve the accuracy of water boundary detection. The F-measure index was used to evaluate the extraction accuracy of the three methods. IMGAC method had the highest extraction accuracy, which was 96.43%. The kappa coefficient reached 0.929. The F-measure index was 96.20%. Our study can provide a reference for water extraction and water boundary optimization.