Damien P. Igoe

Characterization of a smartphone camera's response to ultraviolet A radiation.

As part of a wider study into the use of smartphones as solar ultraviolet radiation monitors, this article characterizes the ultraviolet A (UVA; 320–400 nm) response of a consumer complementary metal oxide semiconductor (CMOS)‐based smartphone image sensor in a controlled laboratory environment. The CMOS image sensor in the camera possesses inherent sensitivity to UVA, and despite the attenuation due to the lens and neutral density and wavelength‐specific bandpass filters, the measured relative UVA irradiances relative to the incident irradiances range from 0.0065% at 380 nm to 0.0051% at 340 nm. In addition, the sensor demonstrates a predictable response to low‐intensity discrete UVA stimuli that can be modelled using the ratio of recorded digital values to the incident UVA irradiance for a given automatic exposure time, and resulting in measurement errors that are typically less than 5%. Our results support the idea that smartphones can be used for scientific monitoring of UVA radiation.

Smartphone based Android app for determining UVA aerosol optical depth and direct solar irradiances

This research describes the development and evaluation of the accuracy and precision of an Android app specifically designed, written and installed on a smartphone for detecting and quantifying incident solar UVA radiation and subsequently, aerosol optical depth at 340 and 380 nm. Earlier studies demonstrated that a smartphone image sensor can detect UVA radiation and the responsivity can be calibrated to measured direct solar irradiance. This current research provides the data collection, calibration, processing, calculations and display all on a smartphone. A very strong coefficient of determination of 0.98 was achieved when the digital response was recalibrated and compared to the Microtops sun photometer direct UVA irradiance observations. The mean percentage discrepancy for derived direct solar irradiance was only 4% and 6% for observations at 380 and 340 nm, respectively, lessening with decreasing solar zenith angle. An 8% mean percent difference discrepancy was observed when comparing aerosol optical depth, also decreasing as solar zenith angle decreases. The results indicate that a specifically designed Android app linking and using a smartphone image sensor, calendar and clock, with additional external narrow bandpass and neutral density filters can be used as a field sensor to evaluate both direct solar UVA irradiance and low aerosol optical depths for areas with low aerosol loads.

Evaluating UVA Aerosol Optical Depth using a Smartphone Camera

This research evaluates a smartphone complementary metal oxide semiconductor (CMOS) image sensors ability to detect and quantify incident solar UVA radiation and subsequently, aerosol optical depth at 340 and 380 nm. Earlier studies revealed that the consumer grade CMOS sensor has inherent UVA sensitivities, despite attenuating effects of the lens. Narrow bandpass and neutral density filters were used to protect the image sensor and to not allow saturation of the solar images produced. Observations were made on clear days, free from clouds. The results of this research demonstrate that there is a definable response to changing solar irradiance and aerosol optical depth can be measured within 5% and 10% error margins at 380 and 340 nm respectively. The greater relative error occurs at lower wavelengths (340 nm) due to increased atmospheric scattering effects, particularly at higher air masses and due to lower signal to noise ratio in the image sensor. The relative error for solar irradiance was under 1% for observations made at 380 nm. The results indicate that the smartphone image sensor, with additional external narrow bandpass and neutral density filters can be used as a field sensor to evaluate solar UVA irradiance and aerosol optical depth.

A method for determining the dark response for scientific imaging with smartphones

The proliferation of smartphone technology has provided an unprecedented opportunity for greater community participation in collaborative scientific observations that were once out of reach due to cost, accessibility, and ease of use. Currently, there have been several applications making use of the various sensors included in a smartphone, particularly the image sensor, which has been used in a wide range of scientific endeavors including air quality and medicine. Like all digital image sensors, the smartphone sensor is subject to noise, particularly that related to dark current. The objective of this article is to present the development and testing of a method to determine the dark response that a smartphone camera may experience under different temperatures representative of the environmental conditions for scientific imaging. This has required the development and testing of a specially developed application. This was tested in the evaluation and analysis of the dark response of a smartphone camera for the range of 8–38°C. The mean of the dark response was relatively unchanged over this range. The method developed in this paper allows the rapid and easy determination of the dark response of smartphone image sensors, enabling this to be readily subtracted from the signal in the development of scientific investigations.

Broadband direct UVA irradiance measurement for clear skies evaluated using a smartphone

UVA wavelengths (320-400 nm) have been implicated in recent studies to contribute to melanoma induction and skin photoaging in humans and damage to plants. The use of smartphones in UVA observations is a way to supplement measurements made by traditional radiometric and spectroradiometric technology. Although the smartphone image sensor is not capable of determining broadband UVA irradiances, these can be reconstructed from narrowband irradiances, which the smartphone, with narrowband and neutral density filters, can quantify with discrepancies not exceeding 5 %. Three models that reconstruct direct broadband clear sky UVA were developed from narrowband irradiances derived from smartphone image sensor pixel data with coefficients of determination of between 0.97 and 0.99. Reasonable accuracy and precision in determining the direct broadband UVA was maintained for observations made with solar zenith angles as high as 70°. The developed method has the potential to increase the uptake of the measurement of broadband UVA irradiances.

Evaluation of a Smartphone Sensor to Broadband and Narrowband Ultraviolet A Radiation

Smartphone image sensor response is compared for broadband and narrowband (340 nm and 380 nm) UVA wavelengths (320–400 nm) based on previous studies that have demonstrated quantitative response to solar radiation at 380 nm and 340 nm to reconstruct broadband irradiance. This article compares broadband and narrowband sensing using a common readily accessible smartphone equipped with a broadband UVA filter that displayed strong sensitivity to long wavelength UVA irradiances from 370 nm with a maximum at 380 nm. However, the use of narrow passband and neutral density filters allowed quantitative observations at the biologically significant wavelength of 340 nm. Narrow passband filter observations also had less variation at 340 nm than observed for broadband measurements. The results indicate that the smartphone image sensor, with the addition of narrow passband and neutral density filters, is a viable tool for UVA observations, but is unsuitable for broadband filter measurements.

Measurements of occupational ultraviolet exposure and the implications of timetabled yard duty for school teachers in Queensland, Australia: preliminary results.

Simultaneous personal measurements of the occupational ultraviolet exposure weighted to the International Commission on Non-Ionising Radiation Protection hazard sensitivity spectrum (UVICNIRP) were made over a five week period (44 person-days) in the second half of the summer school term of 2012 in Queensland, Australia for individual high school teachers located at latitudes of 27.5°S and 23.5°S. These teachers were employed for the duration of the study in a predominately indoor classroom teaching role, excluding mandatory periods of lunch time yard duty and school sport supervisions. Data is presented from personal measurements made to the shirt collar using polyphenylene oxide (PPO) film UV dosimeters. UVICNIRP exposure data is presented for each week of the study period for the shirt collar measurement site and are further expressed relative to the measured ambient horizontal plane exposure. Personal exposures were correlated with time outdoors, showing a higher exposure trend on days when teachers were required to supervise outdoor areas for more than 2h per week (mean daily exposure: 168Jm(-2)UVICNIRP±5Jm(-2) (1σ)) compared to the study average (mean daily exposure: 115Jm(-2)UVICNIRP±91Jm(-2) (1σ)). Time spent in an open playground environment was found to be the most critical factor influencing the occupational UVICNIRP exposure. A linear model was developed showing a correlation (R(2)=0.77) between the time teachers spent on yard duty and UVICNIRP exposure, expressed relative to ambient. The research findings indicate a greater reduction in personal exposure can be achieved by timetabling for yard duty periods in playground areas which offer more shade from trees and surrounding buildings. All mean daily personal exposures measured at the shirt collar site were higher than the ICNIRP occupational daily exposure limit of 30Jm(-2) for outdoor workers.

Characterisation of a smartphone image sensor response to direct solar 305 nm irradiation at high air masses

This research reports the first time the sensitivity, properties and response of a smartphone image sensor that has been used to characterise the photobiologically important direct UVB solar irradiances at 305nm in clear sky conditions at high air masses. Solar images taken from Autumn to Spring were analysed using a custom Python script, written to develop and apply an adaptive threshold to mitigate the effects of both noise and hot-pixel aberrations in the images. The images were taken in an unobstructed area, observing from a solar zenith angle as high as 84° (air mass=9.6) to local solar maximum (up to a solar zenith angle of 23°) to fully develop the calibration model in temperatures that varied from 2°C to 24°C. The mean ozone thickness throughout all observations was 281±18 DU (to 2 standard deviations). A Langley Plot was used to confirm that there were constant atmospheric conditions throughout the observations. The quadratic calibration model developed has a strong correlation between the red colour channel from the smartphone with the Microtops measurements of the direct sun 305nm UV, with a coefficient of determination of 0.998 and very low standard errors. Validation of the model verified the robustness of the method and the model, with an average discrepancy of only 5% between smartphone derived and Microtops observed direct solar irradiances at 305nm. The results demonstrate the effectiveness of using the smartphone image sensor as a means to measure photobiologically important solar UVB radiation. The use of ubiquitous portable technologies, such as smartphones and laptop computers to perform data collection and analysis of solar UVB observations is an example of how scientific investigations can be performed by citizen science based individuals and groups, communities and schools.

Characterization of the corrosion of iron using a smartphone camera

ABSTRACT Smartphone technology provides bountiful opportunities for greater participation in scientific and technological research. Digital camera image sensors have been used for the detection, measurement, and monitoring of corrosion; this work extends that capability to the smartphone. It has been observed that as the corrosion increased in clean iron, red responses decreased proportionally. Green and blue responses quantifiably decreased faster, matching the observed overall reddening as the corrosion increased. Potential noise sources due to the variable texture of the corroded samples had a negligible effect on the results. The effectiveness of this method for the characterization of a smartphone image sensor response to the degree of iron corrosion was reflected in congruent validation tests and errors less than 5%. These results demonstrate that the smartphone may be employed as a low cost and efficient means for the evaluation of surface corrosion.

Detection of ultraviolet B radiation with internal smartphone sensors

ABSTRACT Smartphones have the potential to monitor ultraviolet radiation within the terrestrial solar spectrum. Additionally, the ability to accurately estimate personal ultraviolet exposure using a smartphone may one day allow an individual control of their ultraviolet exposure. Previous studies have demonstrated the detection of ultraviolet A from 320 to 400 nm with a smartphone. However, the measurement of ultraviolet B from 280 to 320 nm is desirable to monitor biological effects such as erythema. No previous reports have been reported for the detection of ultraviolet B detection with a smartphone camera. This study characterized the ultraviolet B response of smartphone cameras and shows that these devices detect this radiation without additional hardware. Three smartphones were tested in the ultraviolet B waveband for dark response, temperature response, irradiance response, and spectral response. The used protocols adhered to international standards where applicable. All characterized smartphones were sensitive to ultraviolet B radiation; however, each type provides a unique response.