WO2006120279A1 - Night-time digital camera and use thereof for automatic all-sky observation - Google Patents

Abstract

The invention relates to a highly-sensitive all-sky night-time digital camera with a range of between 4,000 and 9,500 angstroms. The inventive camera can be used to detect night-time images of the sky such as celestial bodies and transient astrophysical phenomena in the firmament, shooting stars and bolides, night clouds, aircraft and artificial satellites.

Description

TITLE

NIGHT DIGITAL CAMERA AND ITS APPLICATIONS FOR AUTOMATIC OBSERVATION OF ALL THE SKY.

SECTOR OF THE TECHNIQUE

Physical Technology Opto-electronic device for the observation of the night sky continuously with various applications (astrophysics, meteorological and defense field).

STATE OF THE TECHNIQUE

To date, the only products that are known for continuous night sky registration are the following two: 1) the CONCAM camera of the University of Michigan (USA) that is used in several astronomical observatories of the globe that It uses a 1,024 x 1,024 pixel detector to detect stars, with a temporal resolution of 3 minutes, up to magnitude 5.5. (R. J. Nemiroff and J. Bruce Raffert 1999, Towards a continuous record of the sky, PASP 111, 886, http://xxx.lanl.gov/abs/astro-ph/9809403).

2) The Skibotn camera (see more details at http: // www. Des. Lañes. Ac .uk / iono / scasi /) whose objective is the detection of clouds, detecting stars up to magnitude 3. It makes use of a Small size CCD detector (512 x 512 or 1,024 x 1,024 pixels, not specified) and mirror optics to achieve a 180 ° field (Kosch, MJ 1999, The Skibotn CCD AIl -Sky Imager (SCASI) and Real Time Networking onto the World Wide Web. MPAE-T-010-99-12. Max- Planck-Institut für Aeronomie. Lindau, Germany).

Therefore, there is a great need for a digital device for night observation of greater sensitivity, of greater spatial resolution and greater temporal resolution.

DESCRIPTION OF THE INVENTION Brief Description

An object of the invention is a digital camera recording the entire night sky with high sensitivity and angular and temporal resolution and comprising the following components: a) a high resolution astronomical CCD camera as a detector of the images operating in the optical range with at least 2,000 x 2,000 pixels and a pixel size of no more than 9 microns, with an average quantum efficiency above 50%, and sensitive across the entire visible spectral range, between 4,000 and 9,500 angstrots, b) a high brightness fisheye lens as objective lens, located above the camera, to be able to record the whole sky in the CCD detector of a), c) an interface designed specifically to be used to attach the objective lens to the camera CCD, d) a receptacle of suitable dimensions where the CCD detector set, interface and lens are located, and e) a specific software that controls the acquisition of images in the camera from the setting to the at sunrise, the coordination of the different components and the sending of the information to an appropriate peripheral.

A particular object of the present invention consists of a night sky camera system consisting of two or more night cameras of the present invention in the same position such that while in the exposure phase, the second read and save the data, and vice versa.

Another particular object of the present invention consists of a night sky camera system which is constituted by two or more night cameras of the present invention at least 10 kilometers away from each other and that acquire images simultaneously. This would be used to determine the trajectory, due to parallax, of any object that moves less than 5,000 km. away from the earth's surface, which in the case of racing cars, would allow to determine the area of the earth's crust where the corresponding fragments (meteorites) could have fallen. Another object of the present invention is the use of the camera of the present invention for the detection of night images of the celestial vault under suitable conditions corresponding to objects, for illustrative purposes and without limiting the object of the invention, belonging to the following group: celestial bodies and transient astrophysical phenomena in the sky (astronomy), registration of shooting stars and racing cars that could give rise to meteorites that can be recovered (astronomy, geology), night cloud registration (meteorology), registration of flying aircraft the airspace and passage of artificial satellites over a certain place (defense).

DETAILED DESCRIPTION OF THE INVENTION The invention faces the problem of providing new optoelectronic devices for the observation and nocturnal detection of celestial bodies.

The solution provided by this invention is based on the fact that the inventors have observed that it is possible to develop a camera or night observation system of the whole sky ("all-sky camera") of high technical performance by combining a large CCD detector format and a fisheye lens, through an interface and specific software. The advantages of this device Optoelectronic is that it allows observing the whole sky with a sensitivity and an angular resolution superior to the existing ones (with optical magnitudes of at least V = 10 in the zenith, and of at least V = 8 in the horizon), being able to be higher values . For descriptive purposes, V is the magnitude obtained with a filter centered on 5,500 angstrots

(where the human eye has the highest sensitivity) and with a bandwidth of about 900 anglestrms. As an example, the weakest stars that can be discerned with the naked eye on a dark night away from urban centers have magnitude V = 5. A limit magnitude of V = 10 implies being able to detect stars 2,512 ^{10 "5} = 2,512 ⁵ = 100 Sometimes weaker than the naked eye.

Compared to existing devices, described in the prior art, this means: l) a sensitivity between 60 and 600 higher than the cameras described in the prior art, respectively, which means a detection of stars up to magnitude 10 in the zenith (100 times weaker than the human eye records), as well as racing cars, shooting stars, artificial satellites and airplanes.

2) 4-10 times greater precision to locate any celestial object or phenomenon in the sky. This translates, in the case of its use for the registration of racing cars, together with another chamber similar to at least 10 km. away, in a notable reduction of the area of impact on the earth's surface where meteorites could eventually be found in the case of the application of location of the fall of objects (a few square kilometers). With the help of the computer program developed by the inventor, and within the reach of any expert in the field of technology, the automatic image taking of the camera can be controlled according to the duration of the night throughout the year and of Other suitable parameters.

The technology can be applied in various fields: astronomy (detection of celestial bodies and transient astrophysical phenomena in the sky); registration of shooting stars and racing cars that could lead to meteorites that could be recovered; meteorology (night cloud record); defense (registration of airplanes that fly over the airspace and passage of artificial satellites over a certain place), etc.

The acquisition of nocturnal images that can cover the entire celestial vault is one of the demands of the astronomical observatories that currently operate. Being able to have a record of the celestial vault to verify the presence of clouds that prevent astronomical observation in a certain direction of the sky, will allow to optimize the observation time. Being able to register sporadic phenomena such as the case of bright racing cars (meteors) furrowing the sky is something that will undoubtedly report important scientific results. In the latter case, two or more chambers of the invention must be combined to allow by triangulation to locate the exact point of the possible fall of the fragments and recovery - in that case - of the corresponding meteorites.

Therefore, an object of the invention is a digital camera recording the entire night sky, hereinafter night camera of the present invention, with a high sensitivity and angular resolution and comprising the following components: a) a high-resolution astronomical CCD (Charge Coupled Device) digital camera of high spatial resolution, as an image detector operating in the optical range, with at least 2,000 x 2,000 pixels and a pixel size not higher than 9 microns, high resolution, with an average quantum efficiency above 50%, and sensitive in the entire visible spectral range, between 4,000 and 9,500 anglestrom, b) a high luminosity fisheye lens as an objective lens , located above the camera, to be able to record the entire sky in the CCD detector of a), c) an interface designed specifically to be used to attach the objective lens to the CCD camera, d) a receptacle of suitable dimensions where it locates the set of CCD detector, interface and lens, and e) a specific software that controls the acquisition of images in the camera from sunset to sunrise, the coordination of the different components and the sending of the information ion to a suitable peripheral. The astronomical CCD camera used for the camera of the present invention is a digital camera with a range of at least 14 bits (ie to provide a gray scale) that can be selected from those on the market (see example 1), as well as with a high resolution with pixel scale not exceeding 9 microns / pixel, in accordance with the necessary specifications indicated above. A camera of the invention with a very high spatial resolution can be obtained with a CCD camera of 4,096 x 4,096 pixels, of 16 million pixels and a scale of 9 microns / pixel, with a total size of 36 mm on the side or even with one of higher performance

On the other hand, this camera must allow the registration of the celestial vault at reading intervals of 60 seconds or even less in a totally autonomous and remote way. The use of smaller time intervals or temporal resolution, for example, at intervals of 30 seconds, or preferably at intervals of 15 seconds, and more preferably at intervals of 1 second or less, will depend on the technical performance of the new large format cameras that will be developed in the near future based on image transfer technology ("Frame Transfer CCD") and electron multiplication ("Electron Multiplication CCD"). The great advantage of the camera of the invention is that with a reading time of 1 second or less, it will not be necessary to have another camera taking images in parallel to avoid losing temporary information and, more importantly, it will allow to estimate the speed of any object, which is now more complicated due to the high exposure times

(30 s). Currently these FT CCD or EM CCD cameras already mentioned above have a performance of

1,004 x 1002 pixels with one million pixels with an 8 micron / pixel scale and 8 mm side (like that of the Andor house, IXON DV885 model), although in the coming years it is expected to reach levels of about 2,000 x 2,000 pixels and 16 mm side, and even 4,000 x 4,000 pix and 32 mm side longer. Thus, a particular embodiment of the invention is a camera of the invention with a high number of pixels (2,000 x 2,000 pixels) involving a high spatial resolution and at the same time with a reading time of 1 second or less. Similarly, other particular embodiments of the chamber of the invention may be developed depending on the specific needs for each application and the technological capabilities existing in the market, for example, to detect clouds that do not require so much resolution or to detect bodies that They move at high speed or require maximum resolution. On the other hand, another technical option is to find a suitable lens for a smaller detector size (such as the Nikon 10.5 mm f / 2.8 that provides a circular field of 36 mm in diameter or the Coastal 4.88 mm f / 5.6 that provides a circular field of 15 mm in diameter).

The high luminosity fisheye lens used in the camera of the invention as the objective lens has a maximum aperture of f / 5.6, although preferably it could be f / 3.5, or even f / 2.8. The selected photographic objective must be a unique objective that on the detector of this camera can provide an image of the entire celestial vault. In addition, this lens has been modified by lowering the parasol attached 1 cm to avoid the appearance of shadows in the image. Optionally, a heater can be installed around the lens in order to avoid moisture condensation when it exceeds 95%.

To join the two previous components of the camera - objective lens and the CCD camera - that initially are not compatible, an interface designed specifically for each of the possible combinations must be made. In addition, all these elements must be installed in an airtight receptacle of adequate size and shape in each case. Additionally, a fully transparent hemispherical protection (of optical quality) that allows the operation of the night camera outdoors even in adverse weather conditions can be added.

The entire system is controlled with software developed in different languages (for example, in C under Linux environment, see Example 1) operating on a personal computer (for example, Pentium type or similar) without special requirements. The images can be acquired with an exposure time of 30 s which together with the time of necessary reading of another 30 s, supposes a real time to scrutinize the celestial vault of 50%. To achieve the night registration of the celestial vault with 100% effectiveness, it is necessary to use a second camera so that while one is in the exposure phase, the second one reads and records the data, and vice versa.

A particular object of the present invention consists of a night sky camera system that is constituted by two or more night cameras of the present invention in the same position such that while one is in the exposure phase, the second read and save the data, and vice versa. The number of cameras will be based on the opening interval and analysis of the precise information in each camera. Another particular object of the present invention consists of a night sky camera system consisting of two or more night cameras of the present invention at least preferably 10 kilometers away from each other and simultaneously acquiring images. . This would help determine the trajectory, by parallax effect, of any object that travels less than about 5000 km. away from the earth's surface, which in the case of racing cars, will allow to determine the area of the earth's crust where the corresponding fragments could have fallen (for example, meteorites).

Another particular embodiment of the present invention consists of a night camera of the invention in which the astronomical camera consists of a CCD camera that makes use of a 4,096 x 4,096 pixel detector that subtends an area of 36.86 mm x 36.86 mm each pixel having a size of 9 microns, cooled by means of a Peltier system, together with a single objective of 16 mm af / 2.8 modified by lowering the attached sunshade 1 cm to avoid the appearance of shadows on the image with an interface developed in the form of an annular plate 2 mm high, with 50 mm external diameter and 40 mm internal diameter adjusted to the head of the CCD camera and installed in a hermetic cabin - 20 x 20 x 7 cm -in which a central opening has been made in its upper face to install the lens and in its lower face two openings were made, one to allow ventilation of the chamber and the other to connect the corresponding data transmission cable (see Example 1; Figure 1 and 2). The CCD camera used in the present invention is cooled to about 35-40 degrees below room temperature maintaining the operating conditions of the system in a temperature range between -15 ° C to + 35 ° C and humidity between 30 % and 95%, according to their own characteristics and the manufacturer's conditions.

Another object of the present invention is the use of the camera of the present invention for the detection of night images of the celestial vault under suitable conditions corresponding to objects, for illustrative purposes and without limiting the object of the invention, belonging to the following group: celestial bodies and transient astrophysical phenomena in the sky (astronomy), registration of shooting stars and racing cars that could give rise to meteorites that can be recovered (astronomy and geology), registration of night clouds (meteorology), registration of flying aircraft the airspace and passage of artificial satellites over a certain place (defense). DESCRIPTION OF THE FIGURES

Figure 1. - Descriptive scheme of the night camera. Figure 2. Prototype of the "all-sky" camera. The figure shows a real image of a prototype of the chamber of the invention that is located in the Atmospheric Poll Station (ESAt) of the Arenosillo Experimentation Center (INTA-CEDEA) in Mazagón (Huelva). Figure 3. - Image of the entire sky obtained with the camera of the invention. The figure shows an image of the entire sky, with 30 s of exposure, with the zenith in the center of the image and the horizon at the ends. The Milky Way crosses the image diagonally, with Jupiter emerging over the horizon next to some cirrus (left of the image). There is also light pollution from the nearby Mazagón (10 km.) And Huelva (30 km.) In the upper right corner of the image.

Figure 4.- Image of a racing car. The figure shows a part of an image of the whole sky, showing a bright carol crossing the image during the 30 s of exposure made on the celestial vault, which highlights the splendor of our galaxy, the Milky Way, crossing the field.

Figure 5.- Image of an airplane and a racing car. The figure shows part of an image of the "all-sky" camera that shows the light register left by an airplane

(intermittent stroke in the upper left corner of the image) and a racing car appeared simultaneously (center of the image, upper part). The car has a much shorter duration and the evolution of its luminosity is appreciated along the path.

Figure 6.- Image of the antennae of a satellite. The figure shows a fulguration produced by highly reflective antennas of one of the 72 satellites of the Iridium series which located 780 km high, cross the field of vision.

EXAMPLES OF EMBODIMENT In the examples set forth below, the experimentation necessary to develop this patent is detailed, although it should not be construed as limiting it. Example 1.- Construction of the night sky camera and detection of celestial bodies.

The manufacture of the prototype of the camera of the invention has been developed in the following way: a) a refrigerated astronomical CCD camera as an image detector that operates in the large-format optical range, at least 35 mm x 35 mm, and preferably with more than 16 million (4,096 x 4,096 pixels or more), with a quantum efficiency above 50%, and sensitive in the entire visible spectral range, between 4,000 and 9,500 angstrom, b) a high fisheye lens brightness of 10.5 mm focal length and aperture f / 2.8 as the objective lens, located above the camera, to be able to register the entire sky in the CCD detector of a), c) an interface designed specifically based on a ring of 50 mm in diameter and 2 mm in thickness that is used to attach the objective lens to the CCD camera, d) a 30 x 30 x 10 cm sized receptacle where the CCD detector assembly, interface and lens is located, and e) a specific software that controls the acquisition of images in the camera from sunset to sunrise, the coordination of the different components and the sending of the information to a suitable peripheral. For the realization of this particular camera a CCD camera was used as the one manufactured by the American house Apogee, model AP16E that makes use of a 4,096 x 4,096 pixel detector developed by Kodak (model KAF-16801E) that subtends an area of 36.86 mm x 36.86 mm each pixel having a size of 9 microns.

The selected photographic objective must be a unique objective that on the detector of this camera can provide an image of the entire celestial vault. The photographic objective used in this particular embodiment of the invention was the Nikkor AF Fisheye photographic lens of 16 mm to f / 2.8 developed by the Japanese house Nikon. The objective has been modified by lowering the attached sun visor 1 cm to avoid the appearance of shadows in the image.

On the other hand, the adapter ring used to attach the lens to conventional cameras was disassembled and replaced by an interface developed for this purpose: an annular plate 2 mm high, with 50 mm external diameter and 40 mm of internal diameter that was adjusted to the head of the CCD camera with slightly longer screws (1.5 mm) than those that the lens brings as standard.

All this set was installed in a cabin built ex profeso for it, based on a hermetic box of dimensions of 200 mm x 200 mm x 70 mm on which a central opening was made on its upper face to install the lens and on its face Lower two openings were made, one to allow ventilation of the chamber and the other to connect the corresponding data transmission cable (Figure 1 and 2).

The entire system is controlled with software developed in C under a Linux environment operating on a Pentium or similar personal computer. The sky-filled night camera as previously described (see Figure 2) was used for the detection of different celestial bodies from its location in the Atmospheric Sounding Station (ESAt) of the Arenosillo Experimentation Center (INTA-CEDEA) in Mazagón (Huelva).

The following images were acquired with an exposure time of 30 s which together with the necessary reading time of another 30 s, represents a real time to scrutinize the celestial vault of 50%. The detector was cooled to 40 ° C below room temperature using a Peltier system, maintaining the operating conditions of the system in a temperature range between -15 ° C to + 35 ° C and humidity between 30% and 95%, according to its own characteristics and the manufacturer's conditions.

Figure 3 shows a complete picture of the sky, with

30 s of exposure, with the zenith in the center of the image and the horizon at the ends. The Milky Way crosses the image diagonally, with Jupiter emerging over the horizon next to some cirrus (left of the image). Light pollution can also be seen by the nearby Mazagón (10 km.) And Huelva (30 km.) In the upper right corner of the image.

Figure 4 shows a part of an image of the entire sky, showing a bright racing car through the image during the 30 seconds of exposure made on the celestial vault, which highlights the splendor of our galaxy, the Milky Way, crossing the field .

Figure 5 shows part of an image of the "all-sky" camera in which the light register left by an airplane is shown (intermittent trace in the upper left corner of the image) and a racing car appeared simultaneously (center of the image, upper part). The racing car It has a much shorter duration and the evolution of its luminosity along the trajectory is appreciated.

Finally, Figure 6 shows a fulguration produced by highly reflective antennas of one of the 72 satellites of the Iridium series crossing the field of vision.

Claims

1.- Night digital camera characterized in that it comprises the following components: a) an astronomical CCD camera as an image detector that operates in the high-format optical range, high resolution, and with an average quantum efficiency above 50%, and sensitive in the entire visible spectral range, between 4,000 and 9,500 anchors, b) a high-brightness fisheye lens as an objective lens, located above the camera, so that the entire sky can be recorded in the CCD detector of a), c) an interface designed specifically to be used to attach the objective lens to the CCD camera, d) a receptacle of suitable dimensions where the CCD detector set, interface and lens is located, and e) a specific software that controls the acquisition of images in the camera from sunset to sunrise, the coordination of the different components and the sending of the information to a suitable peripheral. 2. - Digital night camera according to claim 1 characterized in that the camera of a) has a resolution of at least 2,000 x 2,000 pixels and therefore 4,000,000 pixels with a total size of more than 16 mm side. 3. Night digital camera according to claim 2 characterized in that the CCD camera of a) has a resolution of 4,096 x 4,096 pixels, 16,777,216 pixels and with a total size of 36.86 mm side. 4. - Digital night camera according to claim 1 characterized in that the camera of a) allows the use of reading time intervals of 30 seconds or less. 5. Digital night camera according to claim 4 characterized in that the camera of a) allows the use of a time interval of 1 second. 6. Night digital camera according to claim 1 characterized in that the camera a) is a camera with a resolution of 4,096 x 4,096 pixels and at the same time allows the use of a reading time interval of 1 second. 7. - Digital night camera according to claim 1, characterized in that the fisheye lens of b) has an aperture of f / 5.6 or less. 8. Night digital camera according to claim 7 characterized in that the aperture is f / 2.8. 9. Night digital camera according to claim 1 characterized in that it has, optionally, a heater installed around the lens. 10. Night digital camera according to claim 1, characterized in that a hemispherical dome of optical quality is attached to the hermetic receptacle of d) to operate outdoors. 11. - Night digital camera according to claim 1 characterized in that the astronomical camera consists of a CCD camera that makes use of a 4,096 x 4,096 pixel detector that subtends an area of 36.86 mm x 36.86 mm each pixel having a size of 9 microns, cooled by a Peltier system, together with a single objective of 16 mm af / 2.8 modified by lowering the attached sunshade 1 cm to avoid the appearance of shadows in the image with an interface developed in the form of an annular plate 2 mm high, with 50 mm external diameter and 40 mm internal diameter adjusted to the head of the CCD camera and installed in an airtight cabin - 20 x 20 x 7 cm -in which a central opening has been made in its upper face to install the lens and in its lower face two openings were made, one to allow ventilation of the camera and the other to connect the corresponding data transmission cable. 12.- Night sky digital camera system characterized in that it is constituted by two or more night digital cameras according to claims 1 to 11 in the same position such that while one is in the exposure phase, another read and record the data, and vice versa. 13.- Night sky digital camera system characterized in that it is constituted by two or more cameras according to claims 1 to 11 with at least 10 kilometers of distance from each other to allow the location and recovery of meteorites or other bodies in the Earth's surface. 14. Use of the digital night camera and digital night camera system according to claims 1 to 12 for the detection of night images of the celestial vault. 15. Use of the digital night camera according to claim 14, characterized in that the images correspond to objects belonging to the following group: celestial bodies, transient astrophysical phenomena in the sky, night clouds, aircraft that fly over the airspace and artificial satellites. 16. Use of the digital night camera system according to claim 13 for the detection in the sky, monitoring and recovery of meteorites on the Earth's surface.