An example forward scatter sensor comprises: a transmitter arranged to emit a single light sheet; a receiver to observe light scattered from particles that fall through a measurement volume; and a control entity comprising an analyzer arranged to record a measurement signal descriptive of intensity of light captured by the receiver as a function of time and to carry out a precipitation analysis on basis of a time segment of the measurement signal, the precipitation analysis comprising: identifying, in said time segment, one or more double peaks that each represent a respective droplet and comprise a first peak that represents light refracted from a bottom of the respective droplet upon entry to the measurement volume and a second peak that represents light reflected from a top of the respective droplet upon exit from the measurement volume; and deriving one or more precipitation parameters and one or more precipitation indications.

The present art applies a unique conceptual model that uses image statistics of top-of-atmosphere reflectance to assess and then reverse atmospheric effects. The workflow first calibrates the method for an Earth observation satellite pre-operationally. Then, for operational conversion of each image of the satellite, the degree of atmospheric effect is mapped across an image to be converted and then reversed to deliver surface reflectance data for each pixel of the image. The resulting surface reflectance images have haze and thin clouds removed, are clarified for viewing and appropriate for automated analyses.

An automated device and a method to carry out visibility measurements are described. The device has an optical system comprising a camera (20), at least one sample image (IMC), and a first flat mirror (S1) and a second flat minor (S2) arranged in mutually different positions in order to generate two reflected images (IM1, IM3) of at least part of the sample image (IMC) at different optical distances with respect to the camera. The device further comprises a processing unit configured to determine a luminance contrast of each of the two reflected images (IM1, IM3) and calculate an instant value representing the visibility from a ratio between the two luminance contrasts.

Several embodiments of an apparatuses and method for sensing objects in a volume of interest are provided, including optionally sensing weather phenomena such as snow, ice, fog and the like by illuminating the volume with a laser pulse which is highly absorbed by the phenomenon and another laser pulse which is highly reflected, and sensing phenomenon presence by the returned pulses. Another aspect involves LIDAR utilizing a plurality of wavelengths. Further aspect include apparatus combining LIDAR and thermal imaging utilizing a single photodetector biased at different polarities to switch between the LIDAR and thermal imaging modes, providing a 3D thermal map of the volume of interest. All features may be combined in a single embodiment of the invention, or various aspects may be combined at will. A dual polarity photodetector for use in such combined LIDAR and thermal imager is also provided. Methods of using various embodiments are also provided.

A method for outputting a control signal can include receiving image data associated with an image captured by an image capture means, determining a visibility condition about a vehicle by analysing at least a portion of the image data to determine one or more edges in the image, and outputting a control signal based on the analysis, the control signal for controlling an operation of a vehicle system of the vehicle. The method may be used to detect the presence of a foggy environment whereby the presence of fog reduces the number of detectable edges in an image.

A passive thermal imaging system includes multiple detector arrays, imaging optics, and processing electronics. Each of the detector arrays include pixels and detect thermal electromagnetic radiation (EMR) within a band around a desired EMR wavelength. The imaging optics receive thermal EMR within the band from an object and image the received thermal EMR from a same region of the object onto pixels of each of the detector arrays. The processing electronics receive a detected signal from each of the pixels of the detector arrays, calculate a correlation value based on a multi-correlation of the received detected signals of corresponding pixels of different detector arrays, and compare the correlation value with a threshold correlation value to determine that a detection event has occurred in response to the correlation value exceeding the threshold correlation value, the threshold correlation value being equal to or between 0.8 and 0.85.

The present disclosure provides to a novel two-target method for measuring the concentration of dust clouds, and an apparatus system that uses the novel two-target method. Cornstarch, corn dust, and saw dust are tested with the apparatus system with the method. This method used the light extinction coefficient of a dust cloud between two targets using a digital camera. This extinction coefficient is linearly related to the concentration of the dust, and the mass extinction coefficient is the key value for this measurement method. The mass extinction efficiency (K) depend greatly on the physical and chemical properties of the dust particles.

A method and system for imaging thermodynamic phase of clouds includes obtaining a spatially-resolved polarimetric image of a region of the sky containing a cloud using a multipixel image sensor having multiple channels corresponding to different wavelength bands, determining a value of the Stokes S.sub.1 polarization parameter of incident light on each pixel corresponding to a portion of the image containing the cloud for multiple channels corresponding to different wavelength bands, and determining the thermodynamic phase of the cloud within the image based on the values of the Stokes S.sub.1 polarization parameter. The Stokes S.sub.1 polarization parameter values determined for a first channel corresponding to a first wavelength band is used to determine a liquid thermodynamic phase, and the Stokes S.sub.1 polarization parameter values determined for a second channel corresponding to a second, shorter wavelength band is used to determine an ice thermodynamic phase.

A method for correcting top-of-atmosphere reflectance data in high altitude imagery to a ground surface reflectance data. Transmission of light through Earth's atmosphere and its suspended load of aerosol particles degrades light within the visible through near infrared portion of the spectrum. This can severely affect the quality of the data recorded by orbiting Earth observation satellites. The method first measures the degree of atmospheric effects upon reflectance, then reverses these effects to deliver surface reflectance data and imagery cleaned of haze and thin clouds.

A method and system for optical vortex transmissometry. The method uses optical orbital angular momentum (OAM) and optical vortices to discriminate coherent non-scattered light from incoherent scattered light. The system includes a laser which transmits a Gaussian laser beam through a medium. An OAM generating device is placed before a photodetector receiver. Coherent, non-scattered light passing through the OAM generating device forms an optical vortex, used to discriminate against the unwanted scattered signal that does not form a vortex. Alternatively, the system includes a transmitter, which generates one or more OAM modes, which are transmitted through a turbid medium. At the receiver, an OAM detection device analyzes the OAM mode spectrum of the received light. Coherent non-scattered light retains the OAM encoded at the transmitter, while scattered light does not. The attenuation of the channel is determined by comparison of the received OAM mode spectrum relative to the transmitted OAM mode spectrum.