Optical remote sensing system for detection of aerial and aquatic fauna

Abstract

A method for determination of a distance from an observation reference point to an object in a measurement volume that can be utilized in a passive optical remote sensing system, and optical remote sensing systems that utilizes the method.

Claims

1. An optical remote sensing system for analysing fauna, comprising an optical system, a detector array, and a signal processor, wherein the optical system is configured for reception of electromagnetic radiation from a measurement volume, wherein the electromagnetic radiation includes electromagnetic radiation having interacted with an object moving through the measurement volume along a trajectory, and the detector array comprises detector elements, each of which provides an output signal in response to received electromagnetic radiation incident upon it, and wherein the optical system and the detector array are arranged with relation to each other so that the optical system directs the received electromagnetic radiation onto the detector elements of the detector array, wherein an object plane of the detector array is focused on the detector array and coincides with the end of the measurement volume, the signal processor is adapted for determination of a distance from the optical system to the object in the measurement volume based on a difference in time between two of the output signals provided by respective detector elements of the detector array in response to received electromagnetic radiation incident upon the respective detector elements and having interacted with the object moving through the measurement volume along the trajectory and based on a time duration of a time period during which the object resides within the measurement volume.

2. The optical remote sensing system according to claim 1, comprising a dark cavity positioned within a field of view of the optical system thereby defining an end of the measurement volume.

3. The optical remote sensing system according to claim 2, wherein the optical system is adjusted so that an image of the dark cavity is focussed onto the detector array.

4. The optical remote sensing system according to claim 1, wherein the detector array comprises a quadrant detector.

5. The optical remote sensing system according to claim 1, wherein the signal processor is adapted for determination of the difference in time based on cross correlation of the two of the output signals.

6. The optical remote sensing system according to claim 1, wherein the signal processor is adapted for determination of direction of movement of the object through the measurement volume based on the difference in time.

7. The optical remote sensing system according claim 1, wherein the signal processor is adapted to determine the distance from the optical system to the object in the in the measurement volume using the equation: $\frac{\hat{r}}{r_o}=\frac{\alpha \frac{2\tau }{\Delta t}}{\left(\alpha -1\right)\frac{2\tau }{\Delta t}+1}$ wherein: ř is the distance from the optical system to the object in the measurement volume, α $\alpha =\frac{{\varnothing }_{\mathrm{tel}}}{d_t}$ is the inverse of the linear scaling coefficient of the measurement volume with the distance r to the optical system, dt, is the width of the field of view of the detector array in its object plane, ∅.sub.tel is the aperture of the optical system, f is the focal length of the optical system, r.sub.o is the distance between the optical system and the object plane of the detector array, Δt is the time duration of the object event, and τ is the difference in time between the two of the output signals provided by the respective detector elements of the detector array.

8. The optical remote sensing system according to claim 1, wherein detector elements of the detector array are positioned along an image of a horizontal trajectory through the measurement volume.

9. The optical remote sensing system according to claim 1, wherein detector elements of the detector array are positioned along an image of a vertical trajectory through the measurement volume.

10. The optical remote sensing system according to claim 1, wherein the optical system comprises a telescope.

11. The optical remote sensing system according to claim 1, comprising at least one source of electromagnetic radiation that is adapted for emission of electromagnetic radiation towards the measurement volume for illumination of the object in the measurement volume.

12. The optical remote sensing system according to claim 11, wherein the at least one source of electromagnetic radiation comprises a laser for emission of a beam of electromagnetic radiation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings illustrate the design and utility of embodiments of the new optical remote sensing system, in which similar elements are referred to by common reference numerals. These drawings are not necessarily drawn to scale. In order to better appreciate how the above-recited and other advantages and objects are obtained, a more particular description of the embodiments will be rendered, which are illustrated in the accompanying drawings. These drawings depict only typical embodiments and are not therefore to be considered limiting of its scope.

(2) In the drawings:

(3) FIG. 1 schematically illustrates a remote sensing system with a Newtonian telescope,

(4) FIG. 2 a) schematically illustrates a front view of a Newtonian aperture,

(5) FIG. 2 b) schematically illustrates in a cross-section seen from above light rays incident on different detector elements of the detector array,

(6) FIG. 2 c) illustrates ray tracing of the field of view of two adjacent detector elements,

(7) FIG. 2 d) shows simulated signals from two adjacent detector elements in response to a particle traversing the measurement volume perpendicular to its length at different distances,

(8) FIG. 3 illustrates east—west time lag correlation of the raytracing of FIG. 2 c),

(9) FIG. 4 is a plot of predicted distance as a function of distance determined by ray tracing,

(10) FIG. 5 schematically illustrates distance accuracy as a function of distance to the object plane of the detector array,

(11) FIG. 6 is a plot of raw and parameterized insect scatter signals,

(12) FIG. 7 shows examples of signals from insects flying through the measurement volume,

(13) FIG. 8 is a scatterplot of object events against predicted range and body intensity, shown together with iso-parametric curves of the inverse square law and the lower detection limit,

(14) FIG. 9 is a scatterplot of insect events; with predicted range {circumflex over (r)} and transit time Δt along the axes. Also plotted is a sliding median of the distribution, as well as the diameter of the measurement volume, and

(15) FIG. 10 shows histograms of the east-west and up-down time lags τ.sub.ew and τ.sub.ud.

DETAILED DESCRIPTION

(16) Various exemplary embodiments are described hereinafter with reference to the figures. It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the optical remote sensing systems and method according to the appended claims or as a limitation on the scope of the claims. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated, or not so explicitly described.

(17) The optical remote sensing system and corresponding methods will now be described more fully hereinafter with reference to the accompanying drawings, in which various types of the optical remote sensing system are shown. The optical remote sensing system may be embodied in different forms not shown in the accompanying drawings and should not be construed as limited to the embodiments and examples set forth herein. For example, the new method is illustrated for a passive optical remote sensing system relying on natural illumination of objects in the measurement volume; however, the method is equally applicable in active optical remote sensing systems comprising one or more sources of electromagnetic radiation for illumination of objects in the measurement volume.

(18) Passive optical remote sensing systems are desirable, since they are very affordable compared to active systems. Typically, they are mobile and simpler to employ, with no concerns for eye-safety since they rely on sunlight or moonlight as their illumination source, and they have much reduced energy consumption compared to their active counterparts.

(19) Drawbacks are that they perform suboptimal without direct sunlight or moonlight, and that there are constraints for the orientation of the measurement volume. For example, with an optical remote sensing system with a telescope, the telescope is preferably pointed towards north on the Northern Hemisphere and towards south on the Southern Hemisphere in order to operate in the preferred backscatter mode.

(20) In the following, the new method is disclosed in connection with a Newtonian telescope in cooperation with a quadrant detector positioned in the image plane of the Newtonian telescope as schematically illustrated in FIG. 1.

(21) FIG. 1 schematically illustrates an optical remote sensing system 10 for analysing fauna, comprising an optical system 12, a detector array 14, and a signal processor 16.

(22) The optical system 12 is a Newtonian telescope 12 with a primary mirror 18 and a secondary mirror 20, wherein the primary mirror 18 and the secondary mirror 20 cooperate to direct received electromagnetic radiation, i.e. electromagnetic radiation incident on the primary mirror 18, from a measurement volume 38 onto the detector array 14 via the beam splitter 22.

(23) The beam splitter 22 is a dichroic beam splitter 22 positioned in front of the detector array 14, which is a Si quadrant detector 14 for detection of electromagnetic radiation ranging from 0.19 μm to 1 μm, and in front of an InGaAs detector 24 for detection of electromagnetic radiation ranging from 0.9 μm to 1.7 μm. The dichroic beam splitter 22 is adapted to transmit SWIR electromagnetic radiation and reflect NIR electromagnetic radiation. These detectors 14, 24 are also capable of resolving wing-beat frequency provided that the sampling frequency is adjusted to be suitable for recording the fundamental wing-beat frequency and preferably also higher harmonics, e.g. sampling frequencies ranging from 10 Hz to 50 kHz. The fundamental wing-beat frequency of some insects is at most 1 kHz.

(24) The dichroic beam splitter 22 and the InGaAs detector 24 are optional and not required for the illustrated optical remote sensing system 10 to operate according to the new method that is further explained below.

(25) When an object 26, such as an insect, moves through the measurement volume along a trajectory 28, the electromagnetic radiation having interacted with the object 26 moving through the measurement volume, is received by the optical system 12, i.e. in the illustrated system 10 the Newtonian telescope.

(26) The Si quadrant detector 14 comprises four detector elements as shown in more detail in FIG. 2 a), each of which provides an output signal in response to electromagnetic radiation incident upon it. The four output signals 30 of the Si quadrant detector 14 and the output signal 32 of the InGaAS detector 24 are connected to a sampling unit 34 that samples and digitizes the output signals with a 20 kHz sampling frequency and transfers the sampled signals to the signal processor 16 of a laptop computer for further processing.

(27) Alternatively, the signal processor 16 may be realized in an integrated circuit, e.g. housed together with the detector array 14, so that the optical remote sensing system 10 may output data on various parameters of objects moving through the measurement volume 38, such as the determined position, direction of movement, wing-beat frequency, etc.

(28) The optical remote sensing system 10 comprises a dark cavity 36, also denoted a termination 36, positioned within the field of view of the Newtonian telescope 12 and defines an end of the measurement volume 38. The illustrated dark cavity 36 is a container with an opening 40 and black inner walls for absorption of electromagnetic radiation. The opening 40 is aligned with the field of view of the detector array 14 of the Newtonian telescope 12 so that reception of background electromagnetic radiation by the telescope 12 is minimized.

(29) The measurement volume 38 is the volume defined by the field of view FOV of the detector array 14 of the telescope 12 indicated by dashed lines 44, 46 between the aperture 42 of the telescope 12 and the opening 40 of the dark cavity 36. In the following, the measurement volume 38 is assumed to be evenly illuminated by sunlight.

(30) The measurement volume 38 is an elongated volume typically several hundred meters long with a diameter of, e.g., 30 cm.

(31) The telescope 12 is focussed at the opening 40 of the dark cavity 36, whereby the object plane of the detector array 14 coincides with the opening 40 of the dark cavity 36 so that an image of the dark cavity 36 is focussed onto the detector array 14. The dotted line 48 indicates the optical axis 48 of the telescope 12.

(32) The signal processor 16 is adapted for determination of a distance from an observation reference point, which in FIG. 1 is defined as the centre 50 of the primary mirror 18 of the telescope 12, to the object 26 in the measurement volume 38, i.e. to a centre 27 of the trajectory 28, based on at least two of the output signals 30 provided by the detector array 14, i.e. the Si quadrant detector 14, in response to received electromagnetic radiation having interacted with the object 26. This is further explained below with reference to FIG. 2.

(33) For example, the signal processor 16 may be adapted for determination of the distance to the object 26 in the measurement volume 38 based on cross-correlation of at least two of the output signals 30 produced by the detector elements of the detector array 14 in response to received electromagnetic radiation having interacted with the object.

(34) In the illustrated optical remote sensing system 10, the signal processor 16 is adapted for calculation of the distance {circumflex over (r)} from the centre 50 of the primary mirror 18 to the object 26, i.e. to a centre 27 of the trajectory 28, in the measurement volume 38 using the equation:

(35) $\begin{array}{cc}\hat{r}=\frac{{\mathrm{\tau \varnothing }}_{\mathrm{tel}}f}{\tau \left(\frac{{\varnothing }_{\mathrm{tel}}f}{r_o}-d_s\right)+\Delta t\frac{d_s}{2}}& \left(1\right)\end{array}$
wherein: ø.sub.tel is the telescope aperture, f is the telescope focal length, d.sub.s is the width of the detector array, r.sub.o is the distance between the observation reference point and the object plane 36 of the detector array 14, Δt is the time duration of object events, and τ is the difference in time between the at least two of the output signals provided by the respective detector elements of the detector array in response to received electromagnetic radiation having interacted with the object moving through the measurement volume along the trajectory, e.g. determined by cross-correlation of the output signals of the respective detector elements.

(36) Obviously, if the observation reference point is moved away from the centre 50 of the primary mirror 18 by a distance d.sub.ref that is positive when the observation reference point is moved towards the measurement volume, the distance {circumflex over (r)} from the displaced observation reference point is calculated using the equation:

(37) $\hat{r}=\frac{{\mathrm{\tau \varnothing }}_{\mathrm{tel}}f}{\tau \left(\frac{{\varnothing }_{\mathrm{tel}}f}{r_o}-d_s\right)+\Delta t\frac{d_s}{2}}-d_{\mathrm{ref}}$

(38) Insects are simulated in a raytracing model of the measurement volume 38 and the ranging equation is devised based on the simulation.

(39) The signal processor 16 is further be adapted for determination of direction of movement of the object 26 through the measurement volume 38 based on at least two of the output signals 30 provided the detector elements of the Si quadrant detector 14 in response to received electromagnetic radiation having interacted with the object 26.

(40) The signal processor 16 is also adapted for determination of a parameter of the received electromagnetic radiation relating to the object 26 in the measurement volume 38 based on at least one output signal 30, 32 provided by a detector 14, 24 of the system 10 in response to received electromagnetic radiation having interacted with the object 26, e.g. based on at least one of the output signals 30 provided by the detector elements of the detector array 14 in response to received electromagnetic radiation having interacted with the object 26.

(41) For example, in addition to counting a number of objects 26, the signal processor 16 is adapted to extract characteristic data for insects moving through the measurement volume 38, such as wing-beat oscillations, spherical scattering coefficient (size), spectral information (in the optical domain) of specific molecules (such as melanin, wax, chitin or haemoglobin), and also of microstructures such as wing membrane thickness.

(42) As illustrated in FIG. 2 a), two of the detector elements of the Si quadrant detector 14 are positioned along an image of a horizontal centre trajectory through the measurement volume 38 at the opening 40 of the dark cavity 36, and two other of the detector elements of the detector array 14 are positioned along an image of a vertical centre trajectory through the measurement volume 38 at the opening 40 of the dark cavity 36.

(43) The optical remote sensing system 10 may comprise a frame (not shown) for supporting the telescope 12 with the detectors 14, 24 and possibly the sampling unit 34.

(44) The illustrated optical remote sensing system 10 is portable.

(45) The optical remote sensing system 10 may comprise a scanner (not shown) that is arranged for moving the frame, e.g. pan and/or tilt and/or pitch and/or traverse the frame, and thereby moving the measurement volume 38.

(46) The signal processor 16 may be adapted for controlling the scanner (not shown) to move the measurement volume 38 to scan a desired volume along a desired moving trajectory, e.g. to perform measurements throughout the desired volume larger than the measurement volume 38; or to perform measurements in sample volumes, e.g. in a regular pattern of volumes separated by volumes wherein no measurements are performed.

(47) The optical remote sensing system 10 may comprise a calibrator (not shown) arranged for placing an object 26 with a known optical characteristic in the measurement volume 38.

(48) The optical remote sensing system 10 may comprise a bandpass filter (not shown) cooperating with the detector array 14 for suppression of background signals and having a centre wavelength within the wavelength range of the detector array 14.

(49) The optical remote sensing system 10 may comprise an additional bandpass filter (not shown) cooperating with the optional additional detector 24 for suppression of background signals and having a centre wavelength within the wavelength range of the detector 24.

(50) Utilization of the new method is further illustrated in FIG. 2.

(51) FIG. 1 a) schematically shows a top view of the Si quadrant detector 14a as mounted to the Newtonian telescope 12 and the dotted arrow 28′ indicates a trace of electromagnetic radiation having interacted with the insect 26 in the measurement volume 38 and impinging on the detector elements of the Si quadrant detector 14a. In the illustrated example and as indicated by the arrow, the insect moves horizontally from east to west through the measurement volume 38, and the electromagnetic radiation impinges on the detector element labelled East first and subsequently impinges on the detector element labelled West. Examples of output signals produced by the detector elements in response to the impinging electromagnetic radiation are shown in FIG. 2 d) as further explained below.

(52) FIG. 2 b) illustrates from above how the two adjacent detector elements labelled East and West, respectively, of the Si quadrant detector 14 receive electromagnetic radiation from slightly different directions through the telescope 12.

(53) FIG. 2 c) illustrates raytracing of the measurement volume 38 of the two adjacent detector elements labelled East and West, respectively. In the upper half of the measurement volume 38, the field of view of the eastern detector element is pale grey and the field of view of the western detector element is dark grey. In the lower half of the measurement volume 38, overlapping fields-of-view are pale grey. The detector array 14, i.e. the Si quadrant detector 14, is focused at the opening 40 of the dark cavity 36 that minimizes reception of background light. Thus, the detector array 14 is de-focussed at the aperture 42 and gradually gets more and more focused along the measurement volume 38 towards the opening 40 that is aligned with the object plane of the detector array 14, of the dark cavity 36. In other words, the field of view of each individual detector element the Si quadrant detector 14 overlaps completely with the other detector element field of views at the aperture 42 of the telescope 12, and the field of views are gradually separated with increased distance to the aperture 42 and at the opening 40 of the dark cavity 36, they are completely separated as the image of the detector element is in focus at the opening 40.

(54) FIG. 2 d) shows examples of simulated output signals produced by the detector elements in response to the impinging electromagnetic radiation as a point scatter moves through the measurement volume 38 horizontally from east to west and perpendicular to the optical axis 48 at a speed of 1 m/s at different distances to the Newtonian telescope 12. The pale grey dotted lines show signals from the detector element labelled East in FIG. 2 a), and the dark grey dotted lines show signals from the detector element labelled West in FIG. 2 a).

(55) Parameters r, τ, and Δt are also shown in FIG. 2 d).

(56) According to the new method, the distance to the object 26 moving through the measurement volume 38 can be calculated from the parameters listed below, four of which are related to the new optical remote sensing system 10, and two of which are related to signals produced by detector elements.

(57) Δt is the transit time, i.e. the time it takes for the object to move through the measurement volume 38. Δt can be determined as part of the parameterization process disclosed in: E. Malmqvist, S. Jansson, S. Török, and M. Brydegaard, “Effective Parameterization of Laser Radar Observations of Atmospheric Fauna,” IEEE Journal of Selected Topics in Quantum Electronics, vol. 22, pp. 1-8, 2016.

(58) τ is the difference in time, i.e. the time lag, between the output signals produced by two respective adjacent detector segments, and is extracted through time lag correlation of the signals. This corresponds to determining the time lag between the signals that yields the highest correlation, i.e. where the signals are the most similar. The east-west time lag correlation of the entire raytracing field in FIG. 2 c) is shown in FIG. 3.

(59) FIG. 2: East-west time lag correlation of the raytracing field from FIG. 2 c). The correlation is at its highest at the time lag where the signals in the eastern and western detector segments are the most similar. Due to the gradual separation of the field of view of the eastern- and western detector segment's with increased distance in the measurement volume 38, τ is a range-dependent parameter that starts out at 0 at close range where the field of view overlap is complete, and ends up at Δt/2 at far range where the field of view separation is complete.

(60) Once these parameters are retrieved from an insect event, they can be inserted into the new ranging equation, equation (1), to calculate the distance between the primary mirror of the telescope and the insect.

(61) $\begin{array}{cc}\hat{r}=\frac{{\mathrm{\tau \varnothing }}_{\mathrm{tel}}f}{\tau \left(\frac{{\varnothing }_{\mathrm{tel}}f}{r_o}-d_s\right)+\Delta t\frac{d_s}{2}}& \left(1\right)\end{array}$

(62) The validity of equation (1) can be evaluated with the simulated insect signals in the raytracing model, where the distance is known. Extracting τ and Δt from the simulated signals and inserting them into equation (1) yields the results illustrated in FIG. 4.

(63) FIG. 3 is a plot used for evaluation of the new ranging equation, where predicted range {circumflex over (r)} is plotted against actual range r. The solid line is a plot of the function y=x. The small deviations arise from the discreet nature of the simulation, and as can be discerned from the plot, the method yields perfect results.

(64) By rearranging equation (1) and introducing the parameter d.sub.t, which is the width of the field of view of the Si quadrant detector 14 in its object plane, see FIG. 2 c), and

(65) $\alpha =\frac{{\varnothing }_{\mathrm{tel}}}{d_t},$
which is the inverse of the linear scaling coefficient of the measurement volume 38 with r, equation (1) can be rewritten as equation (2):

(66) $\begin{array}{cc}\frac{r}{r_o}=\frac{\alpha \frac{2\tau }{\Delta t}}{\left(\alpha -1\right)\frac{2\tau }{\Delta t}+1}& \left(2\right)\end{array}$

(67) If the object plane of the detector array lies in the near field, the measurement volume 38 converges, whereas if the object plane of the detector array lies in the far field, the measurement volume 38 diverges. As such there exists a limit between the near field and far field, r.sub.f, and if the detector array is focused at this limit between the near field and far field r.sub.f, the measurement volume 38 maintains a constant width along its longitudinal direction. In other words, if r.sub.o=r.sub.f, then d.sub.t=ø.sub.tel. Where one decides to terminate the measurement volume 38 therefore has implications on the properties of the new methods, see FIG. 5. With the parameters from FIG. 2, r.sub.f=121.2 m.

(68) FIG. 4 illustrates how the properties of the new method changes with dimensions of the measurement volume 38 with relation to parameters of the telescope 12. When the object plane of the detector array 14 coincides with the limit between the near field and far field, i.e. r.sub.o is equal to r.sub.f, the width of the measurement volume 38 is constant along the longitudinal direction of the measurement volume 38 and the ranging accuracy is unaffected by the distance between the telescope 12 and the trajectory 28 of the insect 26. When the object plane of the detector array is located in the near field, the measurement volume 38 converges and the method becomes less accurate at close range and more accurate at far range, whereas if the object plane of the detector array is located in the far field, the method is more accurate at close range and less accurate at far range.

(69) FIG. 6 shows a detector signal generated in response to an insect moving through the measurement volume 38, together with the body-scatter signal and the result of the parameterization.

(70) FIG. 5 shows examples of insect event time series and power spectra, from which the ranging parameters τ and Δt, the wing-beat frequency f.sub.0, as well as other event parameters have been extracted.

(71) Top: Insect signal with a waveform matching close-range simulation (see FIG. 2 d)). The insect appears in all four detector segments, as expected due to their measurement volume 38 overlapping at close range, and insertion into equation (1) yields a predicted range {circumflex over (r)} of 21 m.

(72) Middle: Signal from an insect impinging on the measurement volume 38 at an inclination, appearing in the upper, lower and western detector segments. The waveform matches mid-range simulation, and insertion into equation (1) yields a predicted range {circumflex over (r)} of 81 m.

(73) Bottom: Insect signal with a waveform matching far-range simulation, appearing in the eastern, western and upper detector segments. Insertion into equation (1) yields a predicted range {circumflex over (r)} of 120 m. The wing-beat frequency f.sub.0 is marked in the power spectrum in all three cases.

(74) Through obtaining the body intensity of each observation, the range-dependent sensitivity of the system 10 can be investigated.

(75) FIG. 8 shows a scatterplot of a large number of events, with predicted range {circumflex over (r)} and body intensity of the observations on the axes together with iso-parametric curves of the inverse square law and the lower detection limit.

(76) The body intensity is strongly tied to the heading of insects—if an insect impinges on the measurement volume 38 at a normal angle, it is observed from the side and thus appears large, while if enters at a high incident angle (i.e. flies along the measurement volume 38) it is observed from the front or back and appears small. In the former case, the insect would also transit the measurement volume 38 quickly, whereas in the latter case it would remain in the measurement volume 38 for an extended period of time. As such, in order to properly evaluate the system sensitivity, the heading angles of insects have to be taken into account. It has been stipulated that the relative strengths of the lower harmonics are tied to the insect heading in relation to the measurement volume 38, and a model has been presented, see M. Brydegaard, “Towards Quantitative Optical Cross Sections in Entomological Laser Radar—Potential of Temporal and Spherical Parameterizations for Identifying Atmospheric Fauna,” PLoS ONE, vol. 10, 2015.

(77) On top of being related to the insect heading, the transit time can be used to evaluate the ranging accuracy.

(78) FIG. 9 is a scatterplot of insect events; with predicted range {circumflex over (r)} and transit time Δt on the axes. Also plotted is a sliding median of the distribution, as well as the diameter of the measurement volume 38. As seen in the figure, the transit time increases with predicted range, as is expected due to the diverging measurement volume 38.

(79) On top of the presented method, other useful information related to insect flight in relation to weather and topography and be extracted from quadrant detectors.

(80) FIG. 10 shows histograms of τ.sub.ew and τ.sub.ud, and the average wind speed in direction during the study period is presented. The east-west distribution is bimodal, indicating that the observed insects intersect the measurement volume 38 laterally, while the up-down distribution is single modal and centred around 0, indicating that vertical movement is limited. Throughout the study period, the wind was mostly blowing westward, with an average wind speed of 1.6 m/s. As such, it can be concluded that the insects fly more with than against the wind in this case.

(81) There are a number of possible uses for the presented method. As disclosed herein, it can be implemented horizontally to profile insects in active or passive mode along a transect over the landscape. This implementation requires shielding off of the background, which can be accomplished by aiming the detector into a dark cavity.

(82) By moving into infra-red wavelength regions where the atmosphere does not transmit sunlight, the method can also be implemented vertically, in which case active illumination is required. The method can then be used to monitor migratory fauna, including birds, bats and insects, and through time lag correlation of the detector segments, the direction of movement, i.e. the flight direction, can be obtained. Ideally, the sensor should be focused at the limit between near- and far field, and the setup parameters should be chosen to ensure that this limit ends up at a suitable distance for the study at hand.

(83) Another approach to vertical profiling would be to fix the aim of the setup at the Polaris star, which would ensure sunlight impinging on the measurement volume 38 at an approximately normal angle at all times. The setup could then be implemented vertically in passive mode.

(84) Detection schemes with multiple wavelength- or polarization bands could also be envisioned, by use of dichroic- or polarization beam splitters, and could be implemented in both active and passive remote sensing systems.

(85) Although particular embodiments have been shown and described, it will be understood that they are not intended to limit the claimed inventions, and it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the claimed inventions. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense. The claimed inventions are intended to cover alternatives, modifications, and equivalents.

(86) With the description above, a person skilled in the art of photonics would be able to carry out the various optical remote sensing systems 10 and methods according to the appended claims. Examples of practical implementation of an optical remote sensing system 10 and data processing can be found in literature, including Mikkel Brydegaard, Aboma Merdasa, Alem Gebru, Hiran Jayaweera, and Sune Svanberg, “Realistic Instrumentation Platform for Active and Passive Optical Remote Sensing,” Appl. Spectrosc. 70, 372-385 (2016), included herein by reference, and Brydegaard, M. (2015): “Towards Quantitative Optical Cross Sections in Entomological Laser Radar—Potential of Temporal and Spherical Parameterizations for Identifying Atmospheric Fauna.” PLOS ONE, DOI: 10.1371/journal.pone.0135231 also included herein by reference, and Mikkel Brydegaard, Alem Gebru, and Sune Svanberg, “Super Resolution Laser Radar with Blinking Atmospheric Particles—Application to Interacting Flying Insects”, Progress In Electromagnetics Research, Vol. 147, 141-151, 2014 also included herein by reference.