Gabor Kovacs | Budapest University of Technology and Economics (original) (raw)

Papers by Gabor Kovacs

SPIE Proceedings, 2013

ABSTRACT Sensitive imaging systems with high dynamic range onboard spacecrafts are susceptible to... more ABSTRACT Sensitive imaging systems with high dynamic range onboard spacecrafts are susceptible to ghost and stray-light effects. During the design phase, the Dawn Framing Camera was laid out and optimized to minimize those unwanted, parasitic effects. However, the requirement of low distortion to the optical design and use of a front-lit focal plane array induced an additional stray light component. This paper presents the ground-based and in-flight procedures characterizing the stray-light artifacts. The in-flight test used the Sun as the stray light source, at different angles of incidence. The spacecraft was commanded to point predefined solar elongation positions, and long exposure images were recorded. The PSNIT function was calculated by the known illumination and the ground based calibration information. In the ground based calibration, several extended and point sources were used with long exposure times in dedicated imaging setups. The tests revealed that the major contribution to the stray light is coming from the ghost reflections between the focal plan array and the band pass interference filters. Various laboratory experiments and computer modeling simulations were carried out to quantify the amount of this effect, including the analysis of the diffractive reflection pattern generated by the imaging sensor. The accurate characterization of the detector reflection pattern is the key to successfully predict the intensity distribution of the ghost image. Based on the results, and the properties of the optical system, a novel correction method is applied in the image processing pipeline. The effect of this correction procedure is also demonstrated with the first images of asteroid Vesta.

Space Science Reviews, Jan 8, 2024

Space Science Reviews, 2024

NASA’s Dawn mission visited the large main-belt asteroids Ceres and Vesta (Russell and Raymond, 2... more NASA’s Dawn mission visited the large main-belt asteroids Ceres and Vesta (Russell and Raymond, 2011), returning a rich data set. Its science and navigation cameras, Framing Cameras 1 and 2, provided more than 100,000 surface images in total of both targets with seven colour and one panchromatic channel. This paper summarizes the scientific calibration
of the Framing Camera images, combining information from on-ground and in-flight
calibration campaigns. We describe the calibration methods, algorithms, and parameters
that led to the final level 1c data product, including correcting stray light sources. In addition, we detail the performance and stability of both instruments.
Keywords: stray-light, ghost image, Dawn FC, calibration, deconvolution, CCD reflection

Color Research & Application, 2001

Abstract Cathode ray tube (CRT) displays are probably the most widely used color imaging devices,... more Abstract Cathode ray tube (CRT) displays are probably the most widely used color imaging devices, and include TV sets and computer monitors. Although the CRT color representations are adequate for people with normal color vision, color-deficient users ...

Science (New York, N.Y.), Jan 23, 2015

Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Chu... more Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Churyumov-Gerasimenko consists of two lobes connected by a short neck. The nucleus has a bulk density less than half that of water. Activity at a distance from the Sun of >3 astronomical units is predominantly from the neck, where jets have been seen consistently. The nucleus rotates about the principal axis of momentum. The surface morphology suggests that the removal of larger volumes of material, possibly via explosive release of subsurface pressure or via creation of overhangs by sublimation, may be a major mass loss process. The shape raises the question of whether the two lobes represent a contact binary formed 4.5 billion years ago, or a single body where a gap has evolved via mass loss.

Proceedings of SPIE - The International Society for Optical Engineering

Nature, 2015

Pits have been observed on many cometary nuclei mapped by spacecraft. It has been argued that com... more Pits have been observed on many cometary nuclei mapped by spacecraft. It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments and models cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts. Alternative mechanisms like explosive activity have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov-Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply...

Sensors, Systems, and Next-Generation Satellites XVII, 2013

ABSTRACT Sensitive imaging systems with high dynamic range onboard spacecrafts are susceptible to... more ABSTRACT Sensitive imaging systems with high dynamic range onboard spacecrafts are susceptible to ghost and stray-light effects. During the design phase, the Dawn Framing Camera was laid out and optimized to minimize those unwanted, parasitic effects. However, the requirement of low distortion to the optical design and use of a front-lit focal plane array induced an additional stray light component. This paper presents the ground-based and in-flight procedures characterizing the stray-light artifacts. The in-flight test used the Sun as the stray light source, at different angles of incidence. The spacecraft was commanded to point predefined solar elongation positions, and long exposure images were recorded. The PSNIT function was calculated by the known illumination and the ground based calibration information. In the ground based calibration, several extended and point sources were used with long exposure times in dedicated imaging setups. The tests revealed that the major contribution to the stray light is coming from the ghost reflections between the focal plan array and the band pass interference filters. Various laboratory experiments and computer modeling simulations were carried out to quantify the amount of this effect, including the analysis of the diffractive reflection pattern generated by the imaging sensor. The accurate characterization of the detector reflection pattern is the key to successfully predict the intensity distribution of the ghost image. Based on the results, and the properties of the optical system, a novel correction method is applied in the image processing pipeline. The effect of this correction procedure is also demonstrated with the first images of asteroid Vesta.

Optometry and Vision Science, 2000

Science (New York, N.Y.), Jan 23, 2015

Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Chu... more Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Churyumov-Gerasimenko consists of two lobes connected by a short neck. The nucleus has a bulk density less than half that of water. Activity at a distance from the Sun of >3 astronomical units is predominantly from the neck, where jets have been seen consistently. The nucleus rotates about the principal axis of momentum. The surface morphology suggests that the removal of larger volumes of material, possibly via explosive release of subsurface pressure or via creation of overhangs by sublimation, may be a major mass loss process. The shape raises the question of whether the two lobes represent a contact binary formed 4.5 billion years ago, or a single body where a gap has evolved via mass loss.

SPIE Proceedings, 2013

ABSTRACT Sensitive imaging systems with high dynamic range onboard spacecrafts are susceptible to... more ABSTRACT Sensitive imaging systems with high dynamic range onboard spacecrafts are susceptible to ghost and stray-light effects. During the design phase, the Dawn Framing Camera was laid out and optimized to minimize those unwanted, parasitic effects. However, the requirement of low distortion to the optical design and use of a front-lit focal plane array induced an additional stray light component. This paper presents the ground-based and in-flight procedures characterizing the stray-light artifacts. The in-flight test used the Sun as the stray light source, at different angles of incidence. The spacecraft was commanded to point predefined solar elongation positions, and long exposure images were recorded. The PSNIT function was calculated by the known illumination and the ground based calibration information. In the ground based calibration, several extended and point sources were used with long exposure times in dedicated imaging setups. The tests revealed that the major contribution to the stray light is coming from the ghost reflections between the focal plan array and the band pass interference filters. Various laboratory experiments and computer modeling simulations were carried out to quantify the amount of this effect, including the analysis of the diffractive reflection pattern generated by the imaging sensor. The accurate characterization of the detector reflection pattern is the key to successfully predict the intensity distribution of the ghost image. Based on the results, and the properties of the optical system, a novel correction method is applied in the image processing pipeline. The effect of this correction procedure is also demonstrated with the first images of asteroid Vesta.

Space Science Reviews, Jan 8, 2024

Space Science Reviews, 2024

NASA’s Dawn mission visited the large main-belt asteroids Ceres and Vesta (Russell and Raymond, 2... more NASA’s Dawn mission visited the large main-belt asteroids Ceres and Vesta (Russell and Raymond, 2011), returning a rich data set. Its science and navigation cameras, Framing Cameras 1 and 2, provided more than 100,000 surface images in total of both targets with seven colour and one panchromatic channel. This paper summarizes the scientific calibration
of the Framing Camera images, combining information from on-ground and in-flight
calibration campaigns. We describe the calibration methods, algorithms, and parameters
that led to the final level 1c data product, including correcting stray light sources. In addition, we detail the performance and stability of both instruments.
Keywords: stray-light, ghost image, Dawn FC, calibration, deconvolution, CCD reflection

Color Research & Application, 2001

Abstract Cathode ray tube (CRT) displays are probably the most widely used color imaging devices,... more Abstract Cathode ray tube (CRT) displays are probably the most widely used color imaging devices, and include TV sets and computer monitors. Although the CRT color representations are adequate for people with normal color vision, color-deficient users ...

Science (New York, N.Y.), Jan 23, 2015

Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Chu... more Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Churyumov-Gerasimenko consists of two lobes connected by a short neck. The nucleus has a bulk density less than half that of water. Activity at a distance from the Sun of >3 astronomical units is predominantly from the neck, where jets have been seen consistently. The nucleus rotates about the principal axis of momentum. The surface morphology suggests that the removal of larger volumes of material, possibly via explosive release of subsurface pressure or via creation of overhangs by sublimation, may be a major mass loss process. The shape raises the question of whether the two lobes represent a contact binary formed 4.5 billion years ago, or a single body where a gap has evolved via mass loss.

Proceedings of SPIE - The International Society for Optical Engineering

Nature, 2015

Pits have been observed on many cometary nuclei mapped by spacecraft. It has been argued that com... more Pits have been observed on many cometary nuclei mapped by spacecraft. It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments and models cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts. Alternative mechanisms like explosive activity have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov-Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply...

Sensors, Systems, and Next-Generation Satellites XVII, 2013

ABSTRACT Sensitive imaging systems with high dynamic range onboard spacecrafts are susceptible to... more ABSTRACT Sensitive imaging systems with high dynamic range onboard spacecrafts are susceptible to ghost and stray-light effects. During the design phase, the Dawn Framing Camera was laid out and optimized to minimize those unwanted, parasitic effects. However, the requirement of low distortion to the optical design and use of a front-lit focal plane array induced an additional stray light component. This paper presents the ground-based and in-flight procedures characterizing the stray-light artifacts. The in-flight test used the Sun as the stray light source, at different angles of incidence. The spacecraft was commanded to point predefined solar elongation positions, and long exposure images were recorded. The PSNIT function was calculated by the known illumination and the ground based calibration information. In the ground based calibration, several extended and point sources were used with long exposure times in dedicated imaging setups. The tests revealed that the major contribution to the stray light is coming from the ghost reflections between the focal plan array and the band pass interference filters. Various laboratory experiments and computer modeling simulations were carried out to quantify the amount of this effect, including the analysis of the diffractive reflection pattern generated by the imaging sensor. The accurate characterization of the detector reflection pattern is the key to successfully predict the intensity distribution of the ghost image. Based on the results, and the properties of the optical system, a novel correction method is applied in the image processing pipeline. The effect of this correction procedure is also demonstrated with the first images of asteroid Vesta.

Optometry and Vision Science, 2000

Science (New York, N.Y.), Jan 23, 2015

Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Chu... more Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Churyumov-Gerasimenko consists of two lobes connected by a short neck. The nucleus has a bulk density less than half that of water. Activity at a distance from the Sun of >3 astronomical units is predominantly from the neck, where jets have been seen consistently. The nucleus rotates about the principal axis of momentum. The surface morphology suggests that the removal of larger volumes of material, possibly via explosive release of subsurface pressure or via creation of overhangs by sublimation, may be a major mass loss process. The shape raises the question of whether the two lobes represent a contact binary formed 4.5 billion years ago, or a single body where a gap has evolved via mass loss.