Subsurface Reflectivity Research Articles

Bathymetry Retrieval From Spaceborne Multispectral Subsurface Reflectance

A few scholars have developed the models for retrieval of water depth from subsurface reflectance of multispectral images to avoid the influences of such as sun glitter. However, the models are only suitable for case I water. For this reason, this study proposes a bathymetry retrieval model using subsurface reflectance for both case I and case II water. The model first corrects the water surface reflectance image and then converts it into a subsurface reflectance image, and the subsurface reflectance image is used as the water depth retrieval image. Landsat 8 images were taken for experiments in case 1 water and case 2 water, and two water areas, Weizhou Island, Guangxi, China, and Molokai Island, Hawaii, USA, were used to verify the proposed model. The experimental results showed that the proposed model reduced the root mean squared error (RMSE) of the retrieved water depth in the Weizhou and Molokai areas from 3.113 m to 2.903 m and 4.239 m to 3.653 m, respectively, i.e., improve accuracy of water depth at 6.75% and 13.82% for Weizhou and Molokai areas, respectively. Therefore, the results demonstrate that the proposed model using subsurface reflectance can significantly improve the accuracy of bathymetry retrieval via spaceborne multispectral images.

Least-Squares Full-Wavefield Reverse Time Migration Using a Modeling Engine With Vector Reflectivity

Conventional least-squares reverse time migration (LSRTM) generally involves a de-migration operator based on the first-order scattering approximation (Born modeling), which can only simulate the seismograms containing the primary reflected wave. When the input observed seismograms contain “redundant information” (especially multiples), crosstalk may occur in the imaging results. Therefore, we develop a least-squares full-wavefield reverse time migration (LSFWM), which is implemented based on a two-way modeling engine with vector reflectivity and the corresponding adjoint sensitive kernel. This modeling engine is modified from the variable density acoustic wave equation and can simulate the subsurface wavefield containing the primaries and multiples only by giving the accurate or estimated subsurface reflectivity and velocity. Theoretically, this LSFWM approach can eliminate the influence of “redundant information” on imaging and provide higher-quality imaging results compared to conventional LSRTM. In addition, since the modeling engine is based on vector reflectivity, the imaging results produced by the LSFWM are also vectorized, which can give more information about the subsurface structures, especially steep structures. And the imaging results produced by the LSFWM can accurately depict the subsurface reflectivity. These are helpful to obtain the information on subsurface structure and physical properties more clearly.

Deep-learning-guided high-resolution subsurface reflectivity imaging with application to ground-penetrating radar data

SUMMARY Subsurface reflectivity imaging is one of the most important geophysical characterization methods for revealing subsurface structures. In many cases, accurate subsurface reflectivity imaging is challenging because of, for example, random or coherent noise in the data and sparse source–receiver observation geometry. We develop a deep-learning-guided iterative imaging method to improve subsurface structure imaging. Specifically, we train a supervised neural network to infer a noise-free, high-resolution image from a noisy, low-resolution image and use this estimated image as guidance to regularize least-squares imaging. We develop a systematic method to generate high-quality synthetic training data (data-label pairs) to train the guidance neural network. The trained neural network can provide high-fidelity predictions even for field-data images that are not in the training data. We validate our new imaging method using one synthetic and two field ground-penetrating radar data examples, and find that our method can produce clean, high-resolution subsurface reflectivity images where existing single-pass and least-squares imaging methods fail due to noise and insufficient data coverage.

Shallow subsurface basalt layer along Cerberus Fossae, Mars: Insights from SHARAD, HiRISE, and CRISM analysis

We surveyed the subsurface structure along Cerberus Fossae using data from SHAllow RADar (SHARAD), High-Resolution Imaging Science Experiment (HiRISE), and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard the Mars Reconnaissance Orbiter (MRO). The subsurface structure along the Cerberus Fossae is fundamental to understanding the depositional history of the region. We identified meter-scale stratigraphy using HiRISE images and digital terrain models (DTMs) and found three distinct vertical units 1) ∼3 to 5 m thick regolith cover, 2) ∼30 m thickly layered unit, and 3) ∼260 m thick massive unit dominated by boulders. Using SHARAD radargrams, we identified a subsurface reflector at the interface between units 2 and 3, located ∼34 m deep. Our analysis suggests a real dielectric permittivity of 9.34 ± 1.01 (1σ), and a mean loss tangent of 0.027 ± 0.01 for the shallow subsurface material, thus indicating thick, dense shergottite-type basaltic material along the Cerberus Fossae. Using the dielectric permittivity mixing law, we found that the porosity of the shergottite-type basalt is ∼4%. CRISM analysis aids in further constraining the nature of the shergottite-type basalt and suggests the presence of Fe-rich olivine along the Cerberus Fossae, thus, referred as olivine-bearing shergottite-type basalt in this study. We derived the age of subsurface material using the crater size-frequency distribution and estimated the crater retention age of ∼4 Ma. Overall, this study suggests a ∼ 30 m thick dense and layered olivine-bearing shergottite-type basalt along the Cerberus Fossae, which is older than 4 Ma. The results of this study are incompatible with the hypothesis of a sea of frozen water in the shallow subsurface (up to 35 m) along the Cerberus Fossae.

Rock glacier composition and structure from radio wave speed analysis with dipping reflector correction

AbstractWe assess the composition and geometry of four individual rock glaciers in Alaska, Wyoming and Colorado by measuring their radio wave speed and applying these results to ground-penetrating radar depth corrections and dielectric mixing models. Our method includes a correction for subsurface reflector dip angle, which we show can lead to an incorrect determination of wave speeds using common midpoint configurations. By observing the radar properties of the rock glaciers and their supraglacial debris, we find that some of the sites exhibit nearly pure ice cores, and all of the sites indicate volumetric ice fractions >50%. These results have implications for terrestrial glaciology and hydrology because the present ice volume is connected to past ice accumulation and subsurface ice preservation, which may affect the future availability of alpine water resources. An understanding of the processes that govern rock glacier evolution over a wide range of latitudes and elevations will also contribute to the exploration of planetary surfaces such as Mars, which hosts a significant population of debris-covered glaciers. Our subsurface composition and geometry estimates will inform simulations of rock glacier formation and evolution to test hypothesized ice origin mechanisms along with the preservation of climate signals.

Algorithms for Evaluation of Biooptical Characteristics in the Gulf of Finland Using Empirical Orthogonal Functions

The paper presents the results of testing the possibility of using empirical orthogonal functions to develop algorithms for estimating the concentration of chlorophyll a and suspended matter, the biomass of cyanobacteria in the eastern part of the Gulf of Finland. To develop the algorithms, we used an array of data from field measurements of the subsurface radiance reflectance in 2012–2014, carried out simultaneously with the determination of bio-optical characteristics. It turned out that in the case of the concentration of chlorophyll a and suspended matter, such algorithms can be created not only using the hyperspectral radiance reflectance, but also for the spectral channels of satellite color scanners MODIS and OLCI. An estimation of the cyanobacteria biomass with the empirical orthogonal functions method is not applicable in the case of using satellite channels. A study of the possibility of the most prone to atmospheric correction errors shortwave MODIS channels exclusion was also made. It turned out that the concentration of chlorophyll a is more sensitive to such exclusion than the concentration of suspended matter. Validation on a MODIS data showed that empirical orthogonal functions algorithms give results no worse than regression ones.

An Improved Method of Surface Clutter Simulation Based on Orbiting Radar in Tianwen‐1 Mars Exploration

AbstractMars Orbiter Subsurface Investigation Radar (MOSIR) is carried by China's first Mars probe, Tianwen‐1 orbiter, investigating the Martian subsurface stratification. Surface clutter from topography off‐nadir will overlap with the subsurface echoes, which affects the recognition of Martian subsurface reflections. Surface clutter simulation can effectively distinguish the nadir and off‐nadir radar echoes. In this paper, we choose the facet method to model the Mars surface topography and combine the roughness parameter with the radar backscatter function. We also provide an analytic expression of the echo phase considering the distance variation in the whole facet. The Chinese first Mars landing site is on Utopia Planitia, which is also one of the key investigating regions of MOSIR. Therefore, we also carried on surface clutter simulation of this region and generated simulation radargram with the Chirp Scaling algorithm. Furthermore, we use the contrast method to compensate for ionospheric error introduced by the NeMars Mars ionosphere model. Our surface clutter simulation program will significantly support MOSIR subsurface investigation, and provide a chance to verify the related data processing.

Sensitivity analysis to near-surface velocity errors of the Kirchhoff single-stack redatuming of multi-coverage seismic data

We present a study of a Kirchhoff-type redatuming approach for irregular multi-coverage land seismic data to remove the disturbing influence of rugged topography and a considerable near-surface velocity inhomogeneity, like a thick weathering layer, on the subsurface reflections. The redatuming method is physically more justified than the commonly used field-static correction methods that provide - in the indicated situation - non-physical temporal adjustments (field statics) by shifting traces in time, which lead to sub-optimal imaging and inversion of the reflections. The redatuming procedure studied here is different: It transforms the multi-coverage seismic reflection data on the irregular measurement surface to a regular measurement configuration on a pre-specified datum, below the inhomogeneous velocity overburden. This is done by stacking/summing the input traces with certain operators or traveltime curves which are calculated by ray tracing. In this way, incoherent subsurface reflections in the input data become coherent and thus recognizable in the output data. To have this happen, the redatuming operation requires a good approximation of the overburden velocity model and a reasonable one of the sub-burden homogeneous velocity model (below the datum). Then the multi-coverage output data on the new flat datum can be imaged and inverted much better than with standard data processing, i.e., with field-static correction. This work is dedicated to explaining the single-stack Kirchhoff-type redatuming approach kinematically using a synthetic model and data based on a real geological situation. However, our main aim is to study the sensitivity of this redatuming method to errors of the overburden velocity model, which is determined from multi-coverage seismic data using first arrivals traveltime tomography commonly used in the oil industry. We apply the redatuming process to a multi-coverage synthetic seismic dataset generated from the models that represent the real geological situation with irregular measurement surfaces and inhomogeneous overburden or near-surface velocity. To assess accuracy, the redatumed data was migrated in depth-domain and the results showed the correct positioning of the reflectors. The results revealed that this redatuming method produces reliable and accurate redatumed data even using approximate velocity models, which can be useful for prestack time and depth imaging.

Comprehensive model for characterizing skin translucency by expert grading, panel evaluation and image analysis in a Chinese population.

Translucent skin is an attribute widely appreciated by people in East Asian countries. There have been studies in the literature to describe the phenomenon by means of clinical grading, instrumental measurement and image analysis. However, due to its subjective and complex nature, skin translucency has not been comprehensively and rigorously characterized and modelled, particularly in the Chinese population. This study is to develop a mathematical model that quantitatively describes skin translucency from visual cues objectively measured from the skin. The study was designed to characterize and model skin translucency by incorporating expert evaluation, panel perception and image analysis of multiple skin visual attributes in one analysis. Faces of 36 Chinese females aged 18-65 years old were evaluated by a dermatologist to obtain clinical translucency scores. Subject pairs were formed with a relatively high and low translucency score in each pair. Their faces were judged in person by 9 panellists in paired-comparison (2-AFC) fashion to pick a 'more translucent skin' from each subject pair. Front-view facial images of the subjects were taken, and multiple colour and other visually perceivable skin attributes were measured using image analysis. Bradley-Terry analysis and multiple regressions were performed to correlate the panel choices of 'more translucent skin' with the objectively measured skin parameters. Multiple skin colour properties affected the panel choices towards translucent skin. Among them skin tone lightness and skin glossiness had positive effects on skin translucency while the hue, colour unevenness, severity of red and dark spots affected it negatively. Subsurface light reflection and skin visual smoothness had some effect but were not statistically significant. A mathematical model was constructed to predict a person's skin translucency from objectively measured skin attributes. The subjective property of skin translucency can be characterized and quantified via a comprehensive modelling process involving clinical grading, panel evaluation, image-based measurement of skin attributes and statistical analysis. A novel skin parameter, Skin Translucency Index (STI) was established, which provides a way to measure skin translucency, making it possible to assess treatment efficacy before and after product application.

An Efficient and Stable High‐Resolution Seismic Imaging Method: Point‐Spread Function Deconvolution

AbstractBy fitting observed data with predicted seismograms, least‐squares migration (LSM) computes a generalized inverse for a subsurface reflectivity model, which can improve image resolution and reduce artifacts caused by incomplete acquisition. However, the large computational cost of LSM required for simulations and migrations limits its wide applications for large‐scale imaging problems. Using point‐spread function (PSF) deconvolution, we present an efficient and stable high‐resolution imaging method. The PSFs are first computed on a coarse grid using local ray‐based Gaussian beam Born modeling and migration. Then, we interpolate the PSFs onto a fine‐image grid and apply a high‐dimensional Gaussian function to attenuate artifacts far away from the PSF centers. With 2D/3D partition of unity, we decompose the traditional adjoint migration results into local images with the same window size as the PSFs. Then, these local images are deconvolved by the PSFs in the wavenumber domain to reduce the effects of the band‐limited source function and compensate for irregular subsurface illumination. The final assembled image is obtained by applying the inverse of the partitions for the deconvolved local images. Numerical examples for both synthetic and field data demonstrate that the proposed PSF deconvolution can significantly improve image resolution and amplitudes for deep structures, while not being sensitive to velocity errors as the data‐domain LSM.

New Insights Into Subsurface Stratigraphy Northwest of Ascraeus Mons, Mars, Using the SHARAD and MARSIS Radar Sounders

AbstractThe Tharsis Montes volcanoes on Mars are the source of laterally extensive lava flows and other volcanic deposits generating a complex stratigraphy throughout the Tharsis Volcanic Province. We use SHAllow RADar (SHARAD) and Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) observations in a region northwest of Ascraeus Mons to determine the composition, density, thickness, and spatial distribution of these emplaced volcanic materials. We identified subsurface reflectors along 43 SHARAD and five MARSIS observations. Reflectors in the volcanic plains are interpreted to be sequences of basaltic lava flows with interspersed pyroclastic material, dust, or regolith during a hiatus in activity. Others correspond to the base of three major flow fields. Several plain reflectors were detected by both MARSIS and SHARAD. Other notable reflectors were identified near Ascraeus' flank where lava buried glacially derived sediment. We derived thickness and other material properties for flows using their distinct topographic boundary visible in the radar images. Permittivity ranged from 7.0 to 11.2 corresponding to lava flow densities of 3.20–3.52 g/cm3. Flow thicknesses ranged from 19.8 to 60.2 m. Loss tangents were low for the flow fields ranging from 0.024 to 0.043. Loss tangents in the plains ranged from 0.010 to 0.076. Higher loss tangents correspond to lossier regions that may have higher concentrations of radar absorbing minerals like hematite. Surface roughness controls where reflectors are detected. SHARAD detects the base of three out of the four flow fields in this region with muted surface roughness from dust mantling and erosion.

The stability of a liquid-water body below the south polar cap of Mars

Radar data from the Mars Express spacecraft show bright subsurface reflections in the Planum Australe area that could be due to liquid water located at a depth of 1.5 km (Orosei et al., 2018). If this interpretation of the data is correct, the presence of such water would have important implications for the present-day thermal state of the region. In this article, we recalculate the depth of the liquid water and we analyze the influence of the regional thermal properties in the surface heat flow and the subsurface temperatures. We have obtained a new depth to the bright reflector between 1.3 and 1.5 km by using a temperature dependent relative permittivity for the water ice and taking into account the dust content in the area. We show that regional properties in the SPLD moderately influence the thermal state of the area where the liquid water is located. A better knowledge of the porosity profile in the studied area is necessary to constrain surface heat flow and subsurface temperatures accurately. Our findings are in agreement with previous work that shows anomalously high local heat flows would be required to sustain liquid water at this location.

Search for shallow subsurface structures in Chryse and Acidalia Planitiae on Mars

Chryse and Acidalia Planitiae (CAP) are known as one of the areas which have abundant sites of recurring slope lineae (RSL) on Mars. We present a radar survey of shallow subsurface structures across the CAP regions using the Mars SHAllow RADar sounder (SHARAD) onboard the Mars Reconnaissance Orbiter (MRO). A total of 25 subsurface reflectors were identified. The detected reflectors do not constitute apparent subsurface structures larger than 30 km. Because those have no counterparts in nearby tracks, we could not suggest that those are real subsurface structures. This study suggests that the CAP region does not have special wide-spread subsurface features which could be linked to the RSL sites.

Optical Coherence Tomography Feedback System for Infrared Laser Sealing of Blood Vessels.

Infrared (IR) lasers have recently been tested as an alternative to electrosurgical and ultrasonic laparoscopic devices for optical sealing of blood vessels. IR laser technology previously demonstrated faster sealing times, reduced thermal spread, and lower device temperatures during experimental studies. However, current commercial laparoscopic devices incorporate electrical impedance and/or temperature sensors as real-time, closed-loop, feedback to indicate successful blood vessel seals. This preliminary study explores an infrared laser system for sealing and optical coherence tomography (OCT) as a potential feedback system for successful vessel seal verification. A 1470-nm diode laser delivered an incident power of 30 W for an irradiation time of 5 s using an 8 × 2 mm linear beam, for creating strong seals in porcine renal blood vessels under compression. After sealing the blood vessels, OCT was performed on unsealed and sealed vessel regions for comparison. Standard vessel burst pressure (BP) measurements confirmed successful seals after OCT. Integrated reflectance intensity in OCT A-scans decreased by an average of 20 ± 6% in sealed versus native vessels of 2.4 ± 0.4 mm diameter. Vessel BP measured 532 ± 239 mmHg, with all vessels (n = 25) recording a successful BP > 180 mmHg (hypertensive blood pressure). Unsealed vessels demonstrated significantly deeper imaging marked by a continuous decay in reflected intensity, while sealed vessels showed subsurface reflectance intensity peaks, immediately followed by a rapid decay in reflectance intensity. These markers are consistent with increased light scattering and decreased optical penetration depth upon thermal coagulation of tissues. A-line OCT data consistently differentiated between sealed and unsealed blood vessel regions. Future work will involve OCT integration into the laparoscopic device for real-time optical feedback during IR laser sealing.

Locating Graves in Different Soil Types and Burial Ages in Pulau Pinang using Ground Penetrating Radar

Ground-penetration radar (GPR) is a geophysical tool widely applied in archaeological and forensic research, such as identifying the exact position of graves. A detailed GPR survey was conducted on the cemeteries in Permatang Pasir and Titi Teras, Penang Island. Moving a 500MHz GPR antenna along parallel transects inside grids was used to collect data. The study’s aim was to present two case studies with varying soil types and burial ages. Analysis of reflection shape, reflection strength and signal polarity helped in the interpretation of burial anomalies. The results varied depending on the soil type; in the sandy field, the GPR investigations were clearer and less complicated than in the clayey sand field. When the conditions are ideal (low conductivity areas with little vegetation), GPR provides highly informative and precise results. Time-slices representations were used as a method to provide details about the subsurface reflection at a certain depth.

Elastic least-squares reverse time migration of steeply dipping structures using prismatic reflections

The migration of prismatic reflections can be used to delineate steeply dipping structures, which is crucial for oil and gas exploration and production. Elastic least-squares reverse time migration (ELSRTM), which considers the effects of elastic wave propagation, can be used to obtain reasonable subsurface reflectivity estimations and interpret multicomponent seismic data. In most cases, we can only obtain a smooth migration model. Thus, conventional ELSRTM, which is based on the first-order Born approximation, considers only primary reflections and cannot resolve steeply dipping structures. To address this issue, we develop an ELSRTM framework, called Pris-ELSRTM, which can jointly image primary and prismatic reflections in multicomponent seismic data. When Pris-ELSRTM is directly applied to multicomponent records, near-vertical structures can be resolved. However, the application of imaging conditions established for prismatic reflections to primary reflections destabilizes the process and leads to severe contamination of the results. Therefore, we further improve the Pris-ELSRTM framework by separating prismatic reflections from recorded multicomponent data. By removing artificial imaging conditions from the normal equation, primary and prismatic reflections can be imaged based on unique imaging conditions. The results of synthetic tests and field data applications demonstrate that the improved Pris-ELSRTM framework produces high-quality images of steeply dipping P- and S-wave velocity structures. However, it is difficult to delineate steep density structures because of the insensitivity of the density to prismatic reflections.

Constraining the depth extent of low-velocity zone along the Chenghai Fault by dense array ambient noise interferometry and horizontal-to-vertical spectral ratio

The depth extent of low velocity fault zones is still a matter of debate due to the lack of vertical resolution for most seismic methods. Autocorrelations and cross-correlations of seismic ambient noise provide us new constraints on this issue by obtaining the shallow subsurface reflections without the need of active sources or earthquakes. The horizontal-to-vertical spectral ratio (HVSR) method can also give constraints on this interface and does not need any extra cost of data collection. In this study, we used one-month continuous seismic data from a dense linear array deployed crossing the Chenghai Fault (CHF) in Yunnan, southwest China. Single station autocorrelation and adjacent station pair cross-correlation methods were used to retrieve body wave reflections from the interface of the shallow crustal low-velocity zone (LVZ). The HVSR method was also performed to delineate the shape of the LVZ. Results show an inverted trapezoidal LVZ which extends to ~1.0 km depth across the fault zone with a lateral extent of ~3 km. Previous studies based on ambient noise surface-wave tomography and teleseismic travel time analysis in the same area show similar characteristics, consistent with the interpretation of our results.

Deconvolución mediante filtro extendido de Kalman para la rigurosa extracción de la reflectividad sísmica

Deconvolution attempts compensating for the distortions affecting a recorded seismogram, increasing its bandwidth and extracting subsurface reflectivity from such seismic trace. The estimated reflectivity needs the highest reliability and resolution because of its subsequent use in the pre-stack seismic processing sequence and seismic inversion. We implemented the predictive deconvolution algorithms, the homomorphic Phase Inversion, and the Extended Kalman Filtering. Their application to synthetic traces extracted reflectivity whose comparison with well-bore allowed comparing the reliability between methods. The algorithms applied to an offshore record provided results whose comparison permitted to analyze the impact of the deconvolution assumptions on each method performance.

A Novel Approach to the Detection and Imaging of Candidate Martian Subglacial Water Bodies by Radar Sounder Data

Research based on Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) data detected unusual radar bright basal reflections located at about 1.5 km depth in a Mars region denoted as Ultimi Scopuli. These reflections were interpreted as a signature of subglacial liquid water even though this interpretation is still being debated in the literature. In this article, we propose a novel approach to the detection and imaging of candidate subglacial liquid water from radar sounding data. The approach combines the radar echo power traces with a suitable digital elevation model to provide a bidimensional representation of the surface. Even if the imaging method reconstructs a representation of the surface, we prove that it can be used to identify subsurface bright reflections in icy regions. Imaging is feasible even if the basal interface is not directly included in the processed data for image generation. To support this experimental evidence, we show that a relationship exists between the value of the reflected echo power originating from the englacial layers and the basal-to-surface-echo-power ratio. The observed relationship holds on both Ultimi Scopuli radar sounding data acquired on Mars and Lake Vostok data acquired on Earth. Our results show that the 2-D imaging provides an alternative way for locating candidate subglacial liquid water bodies on Mars over large areas also where the basal interface is not directly measured. The proposed approach complements previous research for further evaluation of the actual presence of liquid water on Mars.

A Fully Automatic Algorithm for Reflector Detection in Radargrams Based on Continuous Wavelet Transform and Minimum Spanning Tree

Spaceborne radar sounding is a powerful technique in planetary subsurface exploration due to its large penetration ability into loose desiccated materials. Three radar sounders, Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), shallow radar (SHARAD), and Mars Orbiter Subsurface Investigation Radar (MOSIR), are orbiting Mars and have obtained a large quantity of radargrams. These direct observations provide valuable information for deciphering subsurface structure and composition of Mars, which are critical for understanding internal stratigraphy, climate change, and orbital variation in the planet. For this reason, automatic, effective, and precise extraction of subsurface reflectors in radargrams is a prerequisite and remains as a challenge though recent studies have made great progresses. In this study, we propose a fully automatic method for reflector detection in radargrams using transform domain techniques and graph theory. In the preprocessing step, the spatial spectrum information is used to automatically extract region with reflectors in a radargram, which can significantly reduce the computational cost. Then, continuous wavelet transform (CWT) with double threshold is used to detect peaks in each frame, and minimum spanning tree (MST) is further used to connect the peaks based on global information. Our proposed method can quickly reconstruct the reflectors in radargrams with a relatively low tracking error rate, which is better than previous methods based on local information. To testify the effectiveness of the algorithm, we applied our algorithm to SHARAD radargrams in the two polar regions. The results show that more than 90% (80%) of the reflectors can be well-detected in the strong (weak) echo regions, and their subsurface information can be extracted efficiently. Compared with previous methods, our method has a higher degree of automation and a wider applicability. The proposed algorithm can be applied to analyze radargrams over large regions of Mars and other bodies.