High Ambient Noise Levels Research Articles

Machine-learning based detection of marine mammal vocalizations in snapping-shrimp dominated ambient noise

Passive acoustics is an effective method for monitoring marine mammals, facilitating both detection and population estimation. In warm tropical waters, this technique encounters challenges due to the high persistent level of ambient impulsive noise originating from the snapping shrimp present throughout this region. This study presents the development and application of a neural-network based detector for marine-mammal vocalizations in long term acoustic data recorded by us at ten locations in Singapore waters. The detector’s performance is observed to be impeded by the high shrimp noise activity. To counteract this, we investigate several techniques to improve detection capabilities in shrimp noise including the use of simple nonlinear denoisers and a machine-learning based denoiser to suppress the noise level. These are shown to enhance the detection performance significantly. Using the robust detectors developed, we discuss some of the vocalizations detected over three years of our acoustic recorder deployments.

Suspected evening fish chorusing sounds detected in deep waters off Kauai, Hawaii

Noise analyses are crucial to understanding passive acoustic monitoring for marine mammals and their behavioral responses to natural and anthropogenic noises. Suspected biological sounds in the ambient noise data from hydrophones at the Pacific Missile Range Facility (PMRF), Kauai, Hawaii have been found. The sounds are suspected to be chorusing associated with the Deep Scattering Layer (DSL) upward daily vertical migration given they peak around 2 hours after sunset. They have been observed occurring daily including a period in January 2017 when high ambient noise levels during a storm was associated with baleen whale cessation of calling. The sounds occur from 1.4 to 1.8 kHz with the peak near 1650 Hz. They are detectable on multiple broadband hydrophones (21 to 68 km offshore) in deep water (1.5 to 4.7 km), suggesting a large spatial extent. The maximum spectrum level in the 1.6 kHz 1/3rd octave band observed to date was 71 dB re 1 μPa2/Hz. Individual sounds have not been identified to date given the geometries involved and the large spatial extent sensed using deep water hydrophones. These results have similarities to related chorusing research which has suggested a potential link with Myctophidae fishes.

Voice user interfaces in manufacturing logistics: a literature review

AbstractDue to the increasing digitalization in manufacturing logistics, devices to integrate the worker into the digital manufacturing system are necessary. A voice user interface (VUI) can be considered suitable for this purpose due to its flexibility and intuitive operability. Despite the popularity and acceptance of VUIs in everyday life, their use in industrial applications, especially in manufacturing logistics, is still rare. While VUIs have been successfully used in order picking for decades, hardly any other industrial fields of application exist. In this paper, we have identified various barriers to the use of VUI in industrial applications. We categorized them and identified four key barriers. We then conducted a systematic literature review to determine and compare already investigated application areas of VUIs, their characteristics, advantages and disadvantages. We found that in particular the operation of machines and industrial robots, as well as general data and information output on machine and system status, maintenance and employee training are frequently investigated. It is noticeable that VUIs are often used in combination with other user interfaces (UIs). Some challenges to VUI usage, such as high ambient noise levels, have already been solved through various approaches, while other challenges remain. Based on the results of the literature review, we put forward a research agenda regarding further suitable industrial application areas as well as general challenges for the use of VUIs in industrial environments.

Influence of Overpressure Breathing on Vowel Formant Frequencies

Voice controlled management systems are based on speech recognition techniques. The use of such systems in combat aircraft is complex due to a number of critical factors which affect the accuracy of speech recognition, such as high level of ambient noise and vibration, use of oxygen masks, serious psycho-physical stress of speakers, etc. One of the specificity of the oxygen mask application is overpressure breathing. The results of the simulations presented in this paper show that the presence of overpressure on the order of 1000 Pa in the vocal tract has a significant influence on the first two formant frequencies. The formants discrimination field is significantly reduced when oxygen mask is used, influencing both perceptive and automatic discrimination of spoken vowels.

Vocal count responses of narwhals to bulk carrier noise in Milne Inlet, Nunavut, Canada

AbstractConcerns were raised about possible behavioral disturbance to narwhals (Monodon monoceros) when exposed to shipping noise in Milne Inlet, Baffin Island, Canada. We deployed passive acoustic recorders in August and September 2018 and 2019, along and adjacent to the nominal shipping corridor. We measured broadband (0.01–25 kHz) sound pressure levels (SPL) after correcting for the auditory weighting function of high frequency cetaceans. Received SPLs and counts of Whistles, Buzzes, and Knocks were compared in a before‐during‐after study of individual bulk carrier transits, relative to periods with no ships. Narwhal call counts were generally lower once bulk carriers were within line‐of‐sight, including when ship noise levels were just above ambient noise levels. Call counts varied both “before” and “after” individual bulk carriers passed by the recorders. There was no evidence of a behavioral threshold SPL below which a response did not occur. We did not observe call count reductions to the same extent in 2019 compared to 2018 as higher ambient noise levels in 2019 likely masked some individual ship noise. There was no evidence of habituation or sensitization to the bulk carrier noise within or between years. Continued acoustic monitoring is recommended, especially if bulk carrier transits increase.

School Hearing Screening With a Portable, Tablet-Based, Noise-Attenuating Audiometric Headset in Rural Nicaragua.

To investigate the utility and effectiveness of a noise-attenuating, tablet-based mobile health system combined with asynchronous telehealth evaluations for screening rural Nicaraguan schoolchildren for hearing loss. Prospective population-based survey. Rural Nicaraguan communities. There were 3,398 school children 7 to 9 years of age. Diagnostic automated and manual audiometry, detailed asynchronous telehealth evaluations. Referral rates, ambient noise levels, and audiometric results as well as hearing loss prevalence, types, and risk factors. Despite high ambient noise levels during screening (46.7 dBA), no effect of noise on referral rates on automated audiometry or confirmatory manual audiometry in those who failed automated testing was seen. The overall audiometric referral rate was 2.6%. Idiopathic sensorineural hearing loss (SNHL) and cerumen impaction were the most common types of hearing loss in this population with an estimated prevalence of hearing loss (all types) of 18.3 per 1,000 children. SNHL was associated with both drug exposure during pregnancy (p = 0.04) and pesticide exposure in the home (p = 0.03). Hearing screening using a tablet-based, noise-attenuating wireless headset audiometer is feasible and effective in rural low-resource environments with moderately elevated ambient noise levels. The referral rate with noise-attenuating headsets was much lower than that previous reports on this population. In addition, manual audiometry resulted in much lower referral rates than automated audiometry. The confirmed hearing loss rate in this study is comparable to reports from other low-income countries that use some form of noise attenuation during screening. Pesticide exposure and drug exposure during pregnancy are potential causes of SNHL in this population.

Male antiphonal calls and phonotaxis evoked by female courtship calls in the large odorous frog (Odorrana graminea).

Acoustic communication plays a vital role in frog reproduction. In most anuran species, long-distance sound communication is one-way from males to females; during the reproductive season, males produce species-specific advertisement calls to attract gravid females, and females are generally silent but perform phonotactic movements that lead to amplexus. One exception is the concave-eared torrent frog (Odorrana tormota). In this species, females produce courtship calls that elicit antiphonal vocalizations by males, followed by precise phonotactic movements. The large odorous frog O. graminea (previously Odorrana livida) in southern China is subject to the same environmental constraints as O. tormota, with which it is sympatric; it is unclear whether their sound communication is one-way or bidirectional. Here, we provide the first data on female O. graminea vocalizations and their functions. Using playbacks of female calls, we conducted acoustic behavioral experiments in the laboratory in response to which males emitted single- or multi-note antiphonal calls with a varying fundamental frequency. Moreover, they were attracted to female call playbacks, exhibiting precise phonotaxis. The female courtship call-male response interaction thus forms a duet between partners of a receptive pair. These results demonstrate that this unique communication system likely reflects an adaptation to an environment in which short-distance communication is at a premium given the high levels of ambient noise.

An assessment of ambient noise and other environmental variables in a nonhuman primate housing facility.

Acoustic noise and other environmental variables represent potential confounds for animal research. Of relevance to auditory research, sustained high levels of ambient noise may modify hearing sensitivity and decrease well-being among laboratory animals. The present study was conducted to assess environmental conditions in an animal facility that houses nonhuman primates used for auditory research at the Vanderbilt University Medical Center. Sound levels, vibration, temperature, humidity and luminance were recorded using an environmental monitoring device placed inside of an empty cage in a macaque housing room. Recordings lasted 1 week each, at three different locations within the room. Vibration, temperature, humidity and luminance all varied within recommended levels for nonhuman primates, with one exception of low luminance levels in the bottom cage location. Sound levels at each cage location were characterized by a low baseline of 58-62 dB sound pressure level, with transient peaks up to 109 dB sound pressure level. Sound levels differed significantly across locations, but only by about 1.5 dB. The transient peaks beyond recommended sound levels reflected a very low noise dose, but exceeded startle-inducing levels, which could elicit stress responses. Based on these findings, ambient noise levels in the housing rooms in this primate facility are within acceptable levels and unlikely to contribute to hearing deficits in the nonhuman primates. Our results establish normative values for environmental conditions in a primate facility, can be used to inform best practices for nonhuman primate research and care, and form a baseline for future studies of aging and chronic noise exposure.

Optimizing a rapid shutdown module for pre-polarization current in surface nuclear magnetic resonance.

Surface nuclear magnetic resonance (SNMR) technology is widely used for hydrological investigations. At high ambient noise levels, the use of a pre-polarization field can enhance the amplitude of the free induced decay (FID) signal. However, the spatial distribution of the pre-polarization field is inhomogeneous, and so it is vital to optimize the shutdown ramp and time for all combinations of the pre-polarization field amplitude and relative orientation. For this purpose, we designed a rapid and adiabatic shutdown circuit for pre-polarization surface nuclear magnetic resonance (PSNMR) systems. In the initial stage of the shutdown process, the magnetic field energy stored in the direct current transmitting coil is transferred to the capacitor by a semi-controlled full bridge circuit. At the end of the shutdown period, the pre-polarization current decays exponentially toward zero. The shutdown process can be controlled by adjusting the circuit parameters. The shutdown ramp and time of the designed circuit are verified through a series of simulations and experiments. As the initial voltage of the capacitor increases from 65 to 300V, the initial amplitude of the exponential decay of the pre-polarization current increases from 15 to 48A and the shutdown time decreases from 1.4 to 1ms. Our designscheme provides a more reliable concept for the shutdown process in the case of multiple transmitting coils. This allows a larger gain of the FID signal to be obtained in specific PSNMR applications when pre-polarization currents with slightly different channel parameters need to be shutdown uniformly.

Seismic event detection in urban Singapore using a nodal array and frequency domain array detector: earthquakes, blasts and thunderquakes

SUMMARYDetection of seismic events at or below the noise level is enabled by the use of dense arrays of receivers and corresponding advances in data analysis methods. It is not only important to detect tectonic events, but also events from man-made, non-earthquake sources and events that originate from coupling between the solid Earth and the atmosphere. In urban environments with high ambient noise levels the effectiveness of event detection methods is unclear, particularly when deployment restrictions result in an irregular receiver array geometry. Here, we deploy a dense nodal array for 1 month in the highly populated city state of Singapore. We develop a new detection method based on image processing that we call spectrogram stacking, which detects anomalous, coherent spectral energy across the array. It simultaneously detects multiple classes of signal with differing spectral content and aids event classification, so it is particularly useful for signal exploration when signal characteristics are unknown. Our approach detects more local events compared to the traditional short-term average over long-term average and waveform similarity methods, while all methods detect similar numbers of teleseismic and regional earthquakes. Local events are principally man-made non-earthquake sources, with several events from the same location exhibiting repeating waveforms. The closest earthquake occurs in peninsular Malaysia, in an area where no earthquakes have previously been detected. We also detect ground motion over a wide frequency range from discrete thunder events that show complex coupling between acoustic and elastic wavefield propagation. We suggest that care should be taken deciphering local high-frequency tectonic events in areas prone to thunder storms.

BirdNET: A deep learning solution for avian diversity monitoring

Variation in avian diversity in space and time is commonly used as a metric to assess environmental changes. Conventionally, such data were collected by expert observers, but passively collected acoustic data is rapidly emerging as an alternative survey technique. However, efficiently extracting accurate species richness data from large audio datasets has proven challenging. Recent advances in deep artificial neural networks (DNNs) have transformed the field of machine learning, frequently outperforming traditional signal processing techniques in the domain of acoustic event detection and classification. We developed a DNN, called BirdNET, capable of identifying 984 North American and European bird species by sound. Our task-specific model architecture was derived from the family of residual networks (ResNets), consisted of 157 layers with more than 27 million parameters, and was trained using extensive data pre-processing, augmentation, and mixup. We tested the model against three independent datasets: (a) 22,960 single-species recordings; (b) 286 h of fully annotated soundscape data collected by an array of autonomous recording units in a design analogous to what researchers might use to measure avian diversity in a field setting; and (c) 33,670 h of soundscape data from a single high-quality omnidirectional microphone deployed near four eBird hotspots frequented by expert birders. We found that domain-specific data augmentation is key to build models that are robust against high ambient noise levels and can cope with overlapping vocalizations. Task-specific model designs and training regimes for audio event recognition perform on-par with very complex architectures used in other domains (e.g., object detection in images). We also found that high temporal resolution of input spectrograms (short FFT window length) improves the classification performance for bird sounds. In summary, BirdNET achieved a mean average precision of 0.791 for single-species recordings, a F0.5 score of 0.414 for annotated soundscapes, and an average correlation of 0.251 with hotspot observation across 121 species and 4 years of audio data. By enabling the efficient extraction of the vocalizations of many hundreds of bird species from potentially vast amounts of audio data, BirdNET and similar tools have the potential to add tremendous value to existing and future passively collected audio datasets and may transform the field of avian ecology and conservation.

Increased ambient noise and elevated vocal effort contribute to airborne transmission of COVID-19.

Widespread transmission of a novel coronavirus, COVID-19, has caused major public health and economic problems around the world. Significant mitigation efforts have been implemented to reduce the spread of COVID-19 but the role of ambient noise and elevated vocal effort on airborne transmission have not been widely reported. Elevated vocal effort has been shown to increase emission of potentially infectious respiratory droplets, which can remain airborne for up to several hours. Multiple confirmed clusters of COVID-19 transmission were associated with settings where elevated vocal effort is generally required for communication, often due to high ambient noise levels, including crowded bars and restaurants, meat packing facilities, and long-stay nursing homes. Clusters of COVID-19 transmission have been frequently reported in each of these settings. Therefore, analysis of COVID-19 transmission clusters in different settings should consider whether higher ambient noise levels, which are associated with increased vocal effort, may be a contributing factor in those settings. Mitigation strategies that include reduction of ambient noise, softer speech practices, and the use of technology such as microphones and speakers to decrease vocal effort will likely reduce the risk of transmitting COVID-19 or other airborne pathogens.

RespVAD: Voice Activity Detection via Video-Extracted Respiration Patterns

Voice activity detection (VAD) refers to the task of identification of regions of human speech in digital signals such as audio and video. While VAD is a necessary first step in many speech processing systems, it poses challenges when there are high levels of ambient noise during the audio recording. To improve the performance of VAD under such conditions, several methods utilizing the visual information extracted from the region surrounding the mouth/lip region of the speakers' video recording have been proposed. Even though these provide advantages over audio-only methods, they depend on faithful extraction of lip/mouth regions. Motivated by these, a new paradigm for VAD based on the fact that respiration forms the primary source of energy for speech production is proposed. Specifically, an audio-independent VAD technique using the respiration pattern extracted from the speakers' video is developed. The respiration pattern is first extracted from the video focusing on the abdominal-thoracic region of a speaker using an optical flow based method. Subsequently, voice activity is detected from the respiration pattern signal using neural sequence-to-sequence prediction models. The efficacy of the proposed method is demonstrated through experiments on a challenging dataset recorded in real acoustic environments and compared with four previous methods based on audio and visual cues. Data and the code for our implementation will be made available at https://github.com/arnabkmondal/RespVAD.

Evaluation of a stimulus attenuation strategy to reduce stress in hospitalized cats

Hospitalized cats are constantly exposed to unfamiliar and potentially anxiety-producing visual and auditory stimuli. Critical care areas may require heterospecific housing of dogs and cats. For boarding, many veterinary hospitals do not have feline-only wards. In all these conditions, cats are often housed in areas with high volumes of foot traffic and high levels of ambient noise. Attempts to reduce visual stimuli have been carried out. In veterinary hospitals, towels are often hung over the front of the cage. In the shelter environment, when a cardboard box “hide” was provided within the cage, a decrease in behavioral signs of stress has been documented. Unfortunately, these masking devices are not always a practical option in a medical setting because patients are not visible to the technical staff who need to monitor them on a frequent or continual basis. In addition, hiding structures may result in tangling of intravenous lines and monitoring devices. Boxes need to be discarded or sent home after each use; towels need to be disinfected. The aim of this study was to investigate the effect on cat behavior of a cage-front stimulus attenuation strategy that could be easily adapted to any cage. Thirty privately owned cats were individually placed in one of two conjoined cages (left and right), connected via a communicating tunnel inside an isolated study room. Each cage had a cage door. The left or right “start side” was randomly assigned. A previously recorded video of the sights and sounds of a veterinary inpatient ward was projected onto a screen directly in front of the cages for 70 minutes. During this time, starting at the same time each day for 6 consecutive days, each cat was video recorded the entire 70 minutes. On each day, cats could choose between 2 of the following cage front conditions in accordance with a predetermined protocol: unshielded cage front and cage front covered with either a clear plexiglass sheet, or an opaque plexiglass sheet. Time spent on each side was calculated from video recordings of the cats. Two cat-stress scores, established by Kessler and Turner's noninvasive Cat-Stress-Scoring system, were calculated based on each cat's behavior during the first and last 15 minutes of each observation period. The results revealed that, regardless of cage fronts being compared, cats with higher stress scores in the first 15 minutes of the observation spent significantly more time behind the cage front option that allowed for the greatest buffering of external stimuli. In addition, regardless of cage front, cats had a slight preference for the right-sided cage and for the cage they were placed in. Age, sex, and time of the day had no significant influence on cage front preference. These results indicate that cats that experienced elevated levels of stress in a veterinary hospital may benefit from the use of a simple stimulus abatement strategy to attenuate visual and auditory stimuli. Use of a plexiglass sheet at cage front still allows for visualization of the patient by the technical staff.

Mike Buckinghams’s contributions to sub-Arctic acoustics

Mike initiated his research in ocean acoustics and his love affair with aircraft during his tenure with the Royal Aerospace Establishment (RAE). Between 1984 and 1990, he led the RAE effort to characterize and model the ambient noise field in the sub-Arctic (Buckingham, 1987, 1990, and 1994). Mike deployed and monitored sonobuoys from aircraft at several distances from the ice edge. His experiment confirmed Diachok and Winokur’s (1974) observations of a peak in ambient noise levels at the ice edge due to the interaction of ocean waves with sea ice. More importantly, Mike discovered an “enigmatic” intermittent source of high ambient noise levels, which peaked at about 20 Hz, at or near the Greenland glacier. He concluded that the source mechanism was associated with the glacier. In 1990, the Scripps Institution of Oceanography offered Mike a position, in part because of his stimulating pre-offer lecture on ambient noise in the sub-Arctic. As a result of increased melting of glaciers, noise generation at the glacier ocean boundary has become a “hot” research topic. The recent well-designed interdisciplinary experiment of Glowacki et al. (2015) revealed that calving and crashing of glacier blocks into the sea are the most likely cause of Mike’s enigmatic noise.

Loose bolt detection in a complex assembly using a vibro-acoustic sensor array

Abstract A non-destructive testing strategy is proposed that combines microphone measurements and structural measurements in one array. The aim is to lower the total inspection time by reducing the number of structural sensors. This is possible by making use of the easier and faster installation of microphones as compared to structural sensors. Structural sensors are needed to limit the influence of background noise. The proposed algorithm is based on the theory of the Time-Reversal MUltiple SIgnal Classification (TR-MUSIC) algorithm. In addition to the novelty of using a vibro-acoustic array, this publication presents a strategy on how to select only the most ‘valuable’ regions of the frequency spectrum for the TR-MUSIC algorithm and an option to use the algorithm with a number of excitations below the theoretically necessary minimum. The proposed procedure is applied in an experiment that targets the localisation of loose or removed bolts in an assembly of aluminium beams and a honeycomb panel, mounted with rivets, bolts and double-sided tape. Although none of the bolts is in the line of sight of the sensor array, all introduced defects can be found in this experiment. This includes the localisation of multiple defects as well. By adding artificial measurement noise to the microphone measurements, it is demonstrated that a combined vibro-acoustic array can cope with a high ambient noise level, while the process fails if a comparable measurement error is also applied to the structural sensors.

Underwater radiated noise: A new perspective in the Indian Ocean region

ABSTRACTUnderwater Radiated Noise (URN) is an interesting research area both for military as well as non-military applications. The proliferation of submarines particularly by new entrants in the developing world requires far better URN management to effectively achieve the desired acoustic stealth. The ever increasing merchant marine fleet is accompanied with high levels of low frequency ambient noise that interferes with the marine mammal perception of their environment leading to severe Acoustic Habitat Degradation. The Indian Ocean Region (IOR) has particularly become strategically relevant in the twenty-first century with larger presence of warships and merchant marines from across the globe. URN measurement and analysis requires deep understanding of the signal characteristics and fluctuations in the tropical littorals of the IOR. The entire URN management issue needs to be looked at from a comprehensive perspective including policy, technology & innovation and human resource development. URN management requires massive infrastructure and resource investment and given the socio-economic priorities in the region, such resources are hard to get for any long-term strategic vision. The paper attempts to present the fundamental aspects of URN and then discuss the challenges and opportunities in the IOR to ensure safe, secure, sustainable growth for all in the region.

Universal newborn hearing screening in public healthcare in South Africa: Challenges to implementation

Background. The implementation of early hearing detection and intervention (EHDI) remains a challenge in developing countries, despite the known benefits. Objectives. To investigate challenges encountered during implementation of universal newborn hearing screening (UNHS) at a secondary-level public hospital in Johannesburg, South Africa. Methods. A prospective cohort study design that assessed the feasibility of conducting UNHS was adopted. This feasibility assessment was conducted during a 3-month period, and all challenges encountered were identified and documented. Screening time was also recorded for each neonate. Data were entered into Excel, and later analysed using Stata version 11. Results. Of 2 740 neonates born during the study period, 490 (17.9%) were identified for screening, and distortion product otoacoustic emissions screening was conducted on 121 (4.4%). The majority (74.4%) were screened in the first 24 hours of life. Repeat screening was required in 57 (47.1%) neonates, but only 20 returned for follow-up. The most important challenges to the feasibility of UNHS implementation were the insufficient number of audiologists available to provide screening, the high rate of false positive test results and the unacceptably high rates of loss to follow-up. Two modifiable factors, namely the presence of vernix caseosa in the external ear canal and high ambient noise levels, were found to have significantly influenced the screening process. Conclusion. The identified challenges are important considerations for any successful implementation of universal screening protocols. Careful planning to mitigate the challenges will have a positive impact on EHDI initiatives in these contexts.

Analysis and design of the transmitting mode on the pre-polarization surface nuclear magnetic resonance system.

Surface nuclear magnetic resonance (SNMR) technology is widely used in the detection of groundwater due to its non-invasive, qualitative, and quantitative advantages. Nonetheless, SNMR is difficult to employ in a high ambient noise level because of the weak level of nanovolt signals (10-9 V). To solve this problem, pre-polarization (PP) technology is utilized for SNMR detection. That is, the combination of direct current, i.e., PP pulse, with alternating current (AC) pulses is utilized to increase the signal amplitude of shallow hydrogen protons. However, the PP and AC pulses on the same transmitting coil should be output independently when using the PP SNMR system. Meanwhile, to avoid magnetization loss, the process of shutting down the PP field must be both rapid and adiabatic. To solve the above problems, we improved the transmitting part of the PP SNMR system and designed a discharge circuit for PP pulses. The feasibility of the design was demonstrated through both software simulation and actual testing. When the PP current is 91 A, it can be turned off within 3 ms. Via further water measurements in an electromagnetically shielded room, we demonstrated that a PP system with a PP pulse discharge circuit can effectively increase the initial amplitude of the signal.

Performance analysis of adaptive OFDM modulation scheme in VLC vehicular communication network in realistic noise environment

Optical wireless communications (OWC) has emerged as a strong candidate for wireless communications, due to the capacity limitation in the radio frequency (RF) spectrum. Especially visible light communication (VLC) has great potential for short-range outdoor vehicular communications, as vehicle LED lights also transmit data. However, outdoor VLC channels vary fast and, experience multipath scattering and reflection resulting in time domain dispersion. Outdoor VLC links are also subjected to high levels of ambient noise, especially from the sun. Orthogonal frequency-division multiplexing (OFDM), which has proven robustness to multi path fading and noise effects in RF links can also be deployed in VLC links. In this paper, optical OFDM (O-OFDM) along with adaptive modulation scheme is investigated in VLC for vehicle to vehicle (V2V) communications. A (2×2) multiple input multiple output (MIMO) channel, with multiple polarimetric bidirectional reflections and realistic sunlight interference is considered. Two schemes of O-OFDM; direct current biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM) are investigated. Simulation results of the proposed model show increase in data rates up to 50 Mbps along with reduced bit error rate (BER) under both line of sight (LOS) and non-LOS and high noise conditions.