Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0256—Compact construction
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
  • B64G1/00—Cosmonautic vehicles
  • B64G1/10—Artificial satellites; Systems of such satellites; Interplanetary vehicles
  • B64G1/1021—Earth observation satellites
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
  • G01J3/0208—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
  • G01J3/0224—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using polarising or depolarising elements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
  • G01J3/0229—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0294—Multi-channel spectroscopy
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/04—Slit arrangements slit adjustment
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/12—Generating the spectrum; Monochromators
  • G01J3/18—Generating the spectrum; Monochromators using diffraction elements, e.g. grating
  • G01J3/22—Littrow mirror spectrometers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/2803—Investigating the spectrum using photoelectric array detector
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
  • G02B17/02—Catoptric systems, e.g. image erecting and reversing system
  • G02B17/06—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror
  • G02B17/0626—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror using three curved mirrors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
  • B64G1/00—Cosmonautic vehicles
  • B64G1/10—Artificial satellites; Systems of such satellites; Interplanetary vehicles
  • B64G1/1021—Earth observation satellites
  • B64G1/1028—Earth observation satellites using optical means for mapping, surveying or detection, e.g. of intelligence
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
  • B64G1/00—Cosmonautic vehicles
  • B64G1/10—Artificial satellites; Systems of such satellites; Interplanetary vehicles
  • B64G1/1021—Earth observation satellites
  • B64G1/1042—Earth observation satellites specifically adapted for meteorology
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
  • G02B23/02—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices involving prisms or mirrors

Definitions

• the present invention relates to a spectrophotometric device with several spectral bands of measurement, as well as a method for measuring chemical components that are present in the Earth's atmosphere.
• spectrophotometric measurements must be made from a satellite in orbit around the Earth, in spectral bands that contain absorption lines of gaseous carbon compounds, including greenhouse compounds such as carbon dioxide. carbon (CO 2 ) or aerosol compounds.
• the spectrophotometric device that is used must provide an optimal compromise between the number of spectral bands in which spectrophotometric measurements can be made simultaneously, and the weight, the space requirement and than the price of the spectrophotometric device.
• CNES ICSO 2014 "Improved Microcarb concept" Véronique Pascal et al.
• CNES Proposed to use a network-scale spectrometer according to high diffraction orders, in order to cover several narrow spectral bands for analyzing components. atmospheric keys. Since the different diffraction orders are superimposed on the image level of the focal plane, it is necessary to implant a system to separate them. In order to obtain a simpler and more compact instrument, and also to cover a large number of spectral bands, CNES proposed to separate the spectral bands using a cross-network which is inserted in the optical path.
• This network is used to spread the wavelengths in the direction perpendicular to the spectral dispersion direction which is defined by the main scale network. Each order of dispersion of the main network is then projected on a column of the matrix of the detector, the next order being shifted in the perpendicular direction. It is thus possible to acquire all the spectral bands on two matrix detectors in two perpendicular directions.
• CNES also proposed to use the cross network on several orders in order to "bring back" the distant wavelengths on the surface of the detector matrix. But then there is a superposition of diffraction orders and a risk of spurious images, which mitigates the initial advantage of the cross network.
• a first aspect of the invention proposes a spectrophotometric device with several measurement spectral bands, which comprises:
• a telescope having an entrance pupil and an output focal plane, and adapted to focus in the focal plane of exit, radiation that enters this telescope through the entrance pupil;
• a spectrophotometer having an input which is superimposed on the focal plane of exit of the telescope, and comprising a spectral spreading component as well as a matrix detector which is optically conjugated with the input of the spectrophotometer.
• the detector has a photosensitive surface that extends in a first detection direction parallel to a spectral spreading direction produced by the spectral spreading component, and which also extends into a second detection direction perpendicular to the first detection direction.
• the spectrophotometric device further comprises: a pupillary mask disposed in the entrance pupil of the telescope, and having a plurality of apertures forming separate sub-pupils which are respectively dedicated to the measurement spectral bands;
• each pupil separation prism deviates a portion of the radiation which passes through the corresponding sub-pupil in a prismatic deflection direction which is common to all pupil separation prisms, and with a prismatic deviation amplitude which is different from that of each other pupil separation prism, and the spectrophotometer being oriented relative to the pupil separation prisms so that the second detection direction corresponds to optically to the direction of prismatic deflection through the telescope and the spectrophotometer;
• a plurality of possibly curved slots which are distributed in the spectrophotometer inlet so that a longitudinal orientation of each slot optically matches the prismatic deflection direction through the telescope, and the slots are offset with each other so as to receive each through one of the openings in the pupillary mask and one of the pupil separation prisms, and through the telescope, a respective portion of the radiation that comes from a pointing direction of the telescope;
• a first set of filters each determining one of the measurement spectral bands, the filters of the first set being arranged in front of the photosensitive surface of the detector, each filter of the first set being effective inside a detection opening which is superimposed in the second detection direction to an image of only one of the slits, formed by the spectrophotometer with a part of the radiation entering the telescope by only one of the openings of the pupil mask, and the detection aperture of each filter extending in the first direction of detection.
• each spectral band of measurement is determined by one of the openings of the pupil mask which is placed in the entrance pupil of the telescope, by the pupil separation prism and the slot which are associated with this opening of the pupil mask, as well as by one of the filters located in front of the matrix detector.
• the spectrophotometric device thus comprises only one telescope, a single spectrophotometer and a single detector that are common to all spectral bands of measurement. For this reason, the weight, dimensions and price of the spectrophotometric device are reduced relative to the plurality of spectral bands in which spectrophotometric measurements can be made simultaneously. Downstream of the pupillary separation prisms, everything happens as if each band was associated with a different direction of aiming. The registration of the different bands is ensured at the pupil separation prisms.
• the device of the invention thus allows a free choice of the positioning of the spectral bands on the matrix of the detector, an ease of accommodation of a greater number of bands, a good inter-band spectral rejection, and excellent performance of stray light rejection.
• the pupil dimensions can be adapted independently for each band, in particular with a view to a homogenization of the diffraction.
• this it may further comprise at least a second set of filters, which also correspond one-to-one to the spectral bands of measurement. Filters of such a second set may be disposed at the pupil separation prisms, or within the spectrophotometer between the input of the latter and the spectral spreading component. Then, a filter of the first set and a filter of each second set which correspond to the same spectral band are traversed by the same part of the radiation which has entered the telescope by only one of the openings of the pupillary mask.
• the device may also comprise at least one field mask which is arranged near the focal plane of exit of the telescope, or in an intermediate image plane of the telescope.
• Each field mask has apertures that correspond to the slots, or that have images superimposed on the slots, these images being formed by a portion of the telescope that is between the field mask and the telescope's output focal plane, with the radiation entered the telescope through the openings of the pupillary mask.
• the device may further comprise a set of additional prisms, called pupil alignment prisms, which are arranged against the slots.
• the spectral spreading component may be a diffractive grating.
• the spectrophotometer can then be arranged so that the radiation that has entered the telescope through the openings of the pupil mask is reflected by the diffracting grating. Even more preferably, in particular to reduce in an additional measure the space requirement which is due to the spectrophotometer, it may have a so-called quasi-Littrow configuration.
• the radiation that is incident on the diffractive grating and the radiation that emerges from it have optical paths that are close, at least for some of these optical paths.
• the radiation that is incident on the diffractive grating and the radiation that emerges from this same diffractive grating are reflected by the same mirrors of the spectrophotometer, having a collimation function for the incident radiation, and a focusing function for the emerging radiation.
• the device may further comprise a polarization scrambler which is arranged upstream of the entrance pupil of the telescope with respect to a direction of propagation of the radiation in the telescope.
• a polarization scrambler is adapted to mix different polarizations in each part of the radiation that passes through one of the openings of the pupil mask.
• a device which is in accordance with the invention may comprise at least N openings in the pupil mask, N pupil separation prisms, N slots and N filters in each set of filters, and also N pupil alignment prisms on the where appropriate, to enable spectrophotometric measurements to be made simultaneously in N spectral bands, where N is an integer which is between 2 and 12, or equal to 2 or 12, preferably between 4 and 8, or equal to 4 or 8.
• the telescope can be of a type with three mirrors.
• the pupil mask may comprise an additional aperture
• the device may further include an imaging system and a beam splitting component which is disposed in an exit pupil of the telescope. This beam splitting component is then adapted so that an additional portion of the radiation that has entered the telescope through the additional aperture of the pupillary mask is transmitted to the imaging system, while the portions of the radiation that have entered the the telescope through the openings of the pupillary mask thus named so far, are transmitted towards the slots.
• the telescope of the device can thus be common to the spectrophotometer and to an optional imaging channel.
• a second aspect of the invention provides a method for measuring chemical components that are present within a measurement zone in the Earth's atmosphere, which method comprises the following steps:
• IM install a spectrophotometric device with several spectral bands of measurement which is in accordance with the first aspect of the invention, on board a satellite; 121 place the satellite in orbit around the Earth, so that the satellite flies over the measurement area;
• IAI while the pointing direction of the telescope is maintained towards the measurement zone, activate the detector of the spectrophotometer and capture detector pixel reading signals, these read signals providing separately inside geometric bands in the surface photosensitive detector that are optically associated and one-to-one slits through the spectrophotometer, a spectral intensity distribution of radiation that comes from the measurement area in one of the spectral bands of measurement.
• the satellite can be oriented so that the direction The telescope is superimposed on a nadir direction of the satellite during step 141.
• the measurements made can thus relate precisely to a vertical column of atmosphere that lies between the satellite and the terrestrial ground or an ocean surface.
• the satellite may be oriented so that the prismatic deflection direction is perpendicular to a running direction of an image of the measurement area formed by the telescope in the output focal plane during step 141. A such orientation allows to acquire several measuring points juxtaposed perpendicular to the trace in the case of a line of sight which is directed towards the Nadir, while limiting the impact of a yarn effect.
• At least one of the spectral bands of measurement of the device may comprise an absorption line of at least a gaseous carbon compound, such as carbon dioxide or an aerosol compound.
• FIG. 1 is a schematic perspective diagram of a spectrophotometric device with several spectral bands of measurement, which is in accordance with the present invention
• FIG. 2 represents a possible configuration of a pupil mask that can be used in a spectrophotometric device according to the present invention, and which is associated with the pupil separation prisms;
• FIG. 3 is a view in the focal plane of exit of the telescope for a spectrophotometric device according to the present invention
• FIG. 4 illustrates the use of the photosensitive surface of a matrix detector which is used in a spectrophotometric device according to the present invention
• FIG. 5 is a perspective view corresponding to FIG. 3 and showing an implementation of pupil alignment prisms
• FIG. 6 represents an onboard use of a satellite of a spectrophotometric device which is in accordance with the present invention.
• a spectrophotometric device according to the present invention, generally designated 100, comprises a telescope 10 and a spectrophotometer 20.
• the oriented continuous line designated A indicates the optical axis of the device 100, oriented according to the direction of propagation of the radiation.
• the telescope 10 may be of one of the models known to those skilled in the art, for example a model with three mirrors as shown.
• the telescope 10 can form an intermediate image of a scene which is located at a great distance in front of the entry E in the pointing direction DP. This intermediate image is then located in an intermediate focal plane PI of the telescope 10, between the primary mirror 1 1 and the secondary mirror 12 for the type of telescope shown.
• the polarization jammer 15 and the deflection mirror 16 are optional and arranged at the entrance E of the telescope 10.
• only one of these two optical components can be used in the device 100.
• Their implementations are also customary for the device. A person skilled in the art, so that it is not necessary to describe them again.
• the entrance pupil PE is situated upstream of the primary mirror 11 relative to the direction of propagation of the radiation entering through the entrance E in the telescope 10.
• exit pupil PS is the image of the entrance pupil PE by the succession of the three mirrors 1 1, 12 and 13.
• the pupillary mask 17 is disposed in the entrance pupil PE, and has a plurality of separate openings which are distributed within the entrance pupil PE. The positions and dimensions of these openings in the entrance pupil PE can be varied between different embodiments of the device 100, in particular according to radiometric and spectral criteria of the radiation, as well as in terms of space constraints and beam passage through the telescope 10.
• O1-O4 denote four apertures in the pupil mask 17, for a device 100 with four spectral spectrophotometric spectral bands which is used for purposes of illustration herein. description.
• the openings O1-O4 of the pupil mask 17 are dedicated one-to-one to the spectral bands of the spectrophotometric measurements.
• the additional opening O5 which is represented in Figure 2, optional and devoid of pupil separation prism, does not correspond to a spectral spectrophotometric measurement band, and its usefulness will be described later.
• Each of the openings of the pupil mask 17 thus forms a separate sub-pupil inside the entrance pupil PE.
• Pupillary separation prisms are arranged one-to-one against each of the openings 01 -04 of the pupil mask 17, and are designated by the references 31 -34 in FIG. 2 for the example considered at four spectral measurement bands.
• Each of the pupil separation prisms 31-34 completely covers the corresponding aperture of the pupillary mask, so that the beam of radiation passing through this aperture is entirely deflected by the prism, in accordance with the apex angle and orientation of the pupil. this prism. Departures of these deflected beams from the pupil separation prisms 31-34 are shown in broken lines in Figures 1 and 2, and the deflected beams are designated F1-F4. The deviations that are produced by pupil separation premiums 31-34 are different from each other, in at least one direction which is denoted X in FIG. 2.
• These convergence locations in the output focal plane PF are shifted parallel to a direction x which corresponds to the direction X through the reflections on the mirrors 11, 12 and 13. For this reason, the directions X and x can be designated together by prismatic deflection direction.
• a first field mask 18 may be arranged in the intermediate focal plane P1.
• This first field mask 18 has openings which correspond, by optical conjugation through the mirrors 12 and 13, to slots which are arranged in the output focal plane PF and are described later.
• Such a first field mask 18 limits the useful field of the device 100 around the pointing direction DP, with peripheral margins to avoid obscuring useful parts of the beams of radiation that come from the apertures 01 -04 of the pupil mask 17, including the additional opening 05 as appropriate.
• the optional component 19 which is arranged in the exit pupil PS may be a simple folding mirror of the F1-F4 radiation beams. But when the pupillary mask 17 has the additional opening 05, the component 19 can be adapted to direct the beam of radiation which comes from this additional opening 05, designated F5 in FIG. 2, towards an annex imaging system 60 , separately from other F1-F4 beams from openings 01 -04. For this reason, component 1 9 has been referred to as a beam splitting component in the general part of this specification.
• the imaging system 60 also optional, can then capture an image that is formed by the telescope 10 of scene content that is in the pointing direction DP.
• the beam splitting component 19 may be a plane mirror with an opening O 'which is located in the exit pupil PS at the location of the image of the additional opening 05 which is formed by the mirrors 1 1, 12 and 13.
• an annex mirror 61 is used between the beam splitting component 19 and the imaging system 60. It is further recalled that the imaging path which consists of the additional aperture 05 of the pupil mask 17, the beam splitting component 19, the imaging system 60 with the fallback mirror 61, if applicable, is not essential to the invention, nor related to the principle thereof.
• this imaging path it may be advantageous to suppress the effect of polarization scrambler 15 in the additional aperture 05, for example by providing a hole in the polarization scrambler 15 at the beam passing location. F5 radiation that enters the telescope 10 through the additional aperture 05.
• a slit mask 40 is disposed in the focal plane of exit PF of the telescope 10.
• FIG. 3 is thus a plan view of this mask 40. It is opaque for the radiation outside the slits, and has as many slits as the number of spectral bands of the device 100.
• the slots, designated by the references 41 -44, are arranged at the locations of convergence of the F1-F4 radiation beams which are respectively from the openings 01 -04 of the pupil mask 17 having been deviated by pupil separation prisms 31 -34.
• the slots 41 -44 are therefore offset with each other in the direction of prismatic deflection x, and are further longitudinally oriented substantially in this direction.
• the offsets between the slots 41 -44 parallel to the x direction are thus determined by the apex angles of the pupil separation prisms 31 - 34. All the slots 41 -44 preferably have the same length, but two successive slits in the x direction can eventually meet to form a continuous slot.
• the slots 41-44 may be slightly curved so that they follow a field curvature which is due to the spectrophotometer 20.
• this field curvature of the spectrophotometer 20 can be compensated for by an identical field curvature which is produced by the telescope 10.
• Another field mask may be located upstream of the slot mask 40 with respect to the direction of propagation of the radiation, a few millimeters in front of this slot mask 40.
• This other field mask has openings corresponding to the slots 41-44, and further limits the useful field of the device 100 around the pointing direction DP.
• the spectrophotometer 20 may be one of the types known to those skilled in the art, but a quasi-Littrow type configuration is particularly advantageous for reducing the bulk that is caused by the spectrophotometer.
• the spectrophotometer 20 may comprise three mirrors 21, 22 and 23 for collimating the F1-F4 radiation beams that come from the slots 41 -44, a diffracting echelette grating 24 operating in reflection, and a matrix image detector 26.
• the ladder diffractive grating 24 forms the spectral spreading component mentioned in the general part of the present description.
• the F1-F4 beams that are derived from the slots 41 -44 are reflected by the diffractive grating 24. to the succession of the mirrors 21 -23, according to an optical path which is close to that traveled to reach the diffractive grating 24 from the slots 41 - 44, but with a direction of propagation of the radiation which is inverse.
• the slots 41-44 are then imaged by the spectrophotometer 20 on the photosensitive surface of the detector 26.
• the grating 24 produces a diffraction of the F1-F4 radiation beams which are derived from the slots 41 -44, resulting in a spread of the image each of the slots 41-44 on the detector 26, parallel to a common direction called spectral spreading direction.
• the spectrophotometer 20 is oriented relative to the pupil separation prisms 31-34 so that the spectral spreading direction is perpendicular to the image of the prismatic deflection direction x which is formed by the spectrophotometer 20 on the detector 26.
• FIG. 4 shows the image content that thus appears on the photosensitive surface of the detector 26.
• the spectrophotometer 20 consists of four geometric strips B1-B4 which are each taken from the image of one of the slots 41 -44 through the spectrophotometer 20 Each geometric band therefore has as a basis the image of the corresponding slot, and extends parallel to the direction of spectral spreading.
• the geometric strips B1-B4 are offset relative to each other perpendicular to the spectral spreading direction in accordance with the prismatic deviations which are produced by pupil separation prisms 31-34.
• the direction of spectral spreading has been called the first direction of detection in the general part of the present description, and is denoted D1 in FIG. 4.
• the direction perpendicular to D1, denoted D2 and called second direction of detection is optically conjugated with the direction of prismatic deviation x.
• the assignment of the geometric bands B1-B4 which are thus formed on the photosensitive surface of the detector 26, to spectral bands of spectrophotometric measurements, is performed by a set of filters 27, said first set of filters.
• the filters of the assembly 27 are held just in front of the photosensitive surface of the detector 26, and each filter covers the entire corresponding geometric band.
• the radiation that is detected by the detector 26 in one of the geometric bands B1 -B4 is limited to the spectral bandwidth of that of the filters of the assembly 27 which covers this geometric band.
• the passage of a pixel from the photosensitive surface of the detector 26 to the next pixel in the detection direction D1 corresponds to a wavelength variation within the spectral band of that of the filters under which these pixels are located.
• the reading of the pixels of the same column of the detector 26, parallel to the detection direction D1 inside one of the geometric bands B1 -B4, provides an evaluation of the spectral distribution of intensity of the radiation in the spectral band that corresponds to this geometric band.
• the transition from one spectral spectrophotometric measurement band to another corresponds to a displacement in the detection direction D2 to change the geometric band.
• the useful field of the device 100 around the pointing direction DP is limited by the lengths of the slots 41 -44, but it can be further limited by a selection along the detection direction D2, pixels that are actually read inside each of the B1 -B4 geometric bands.
• the read signals that come from pixels selected and aligned in the detection direction D2, but which belong to one of the geometric bands B1 -B4, can be added to increase the signal-to-noise ratio.
• several groups of adjacent pixels can be made, which makes it possible to have spatial information and thus measurements on adjacent atmosphere columns.
• additional sets of filters that have spectral characteristics identical to those of the filters of the first set 27, can be arranged at the entrance pupil PE of the telescope 10 and at the slots 41 -44, or only at only one of these two locations.
• Such additional filters which are arranged at the level of the entrance pupil PE are assigned one-to-one to each of the openings O1-O4 of the pupil mask 17.
• they may be carried by the pupil separation prisms 31 - 34.
• the additional filter that is assigned to each of the openings 01 -04 must be identical or compatible with the filter of the assembly 27 by following that of the beams of radiation F1-F4 which is derived from this opening through the device 100 to the detector 26. The same This condition applies to additional filters that are arranged at or near the slots 41-44.
• FIG. 1 further shows two optional deflection mirrors 25a and 25b, which are used to offset laterally with respect to the mirror 21, in opposite directions, the slot mask 40 on the one hand, and the detector 26 with the set of filters 27 on the other hand.
• the reflecting mirror 25a is located between the slit mask 40 and the mirror 21, and along the path of the radiation beams F1-F4.
• the deflection mirror 25b is located between the mirror 21 and the filter assembly 27.
• An optical window of the cryostat which is traversed by the F1-F4 radiation beams from the tertiary mirror 13 of the telescope 10, can be located between the exit pupil PS and the focal point of exit PF of the telescope 10.
• Such a window of cryostat is designated 30 in FIG.
• the radiation beams F1 -F4 which form the geometric bands B1 -B4 on the detector 26 can be moved transversely away from each other.
• the diffracting grating 24 It is then possible for these distances between beams to require the diffracting grating 24 to have large dimensions, causing an annoying bulk, or even a sufficiently large diffractive grating can not be manufactured.
• additional prisms 51-54 referred to as pupil alignment prisms and visible in FIG. 5, can be arranged one-to-one against the slots 41 -44, preferably on the side of the spectrophotometer 20.
• each of the pupillary alignment prisms 51-54 may carry an additional filter as mentioned above, in agreement with the spectral measuring band which corresponds to the slot against which this pupil alignment prism is arranged.
• each pupillary alignment prism may be slightly inclined to superpose more precisely the entrance pupil of the spectrophotometer 20 to the images which are formed by the telescope 10 of the openings O1-O4 of the pupil mask 17, corresponding to exit sub-pupils. of the telescope.
• An aperture mask 28 may also be disposed downstream of pupil alignment prisms 51-54 relative to the direction of propagation of the radiation, a few millimeters from the prisms 51-54, to suppress parasitic portions of radiation that would result from unwanted reflections. on the faces of prisms 51-54.
• the spectral bands of spectrophotometric measurements of the device 100 may be located in the near infrared. These spectral bands may be, for example: [757.8 nm; 767.5 nm] for band B1, [1593.8 nm; 1717.2 nm] for the B2 band, [2018.8 nm; 2048.5 nm] for B3 band, and [1782.4 nm; 1707.0 nm] for the B4 band. These spectral bands are particularly suitable for a space mission characterizing the gaseous flows of carbon compounds that occur on the surface of the Earth.
• focal length of the telescope 10 of the order of 122 mm dimensions of the entrance pupil of the telescope 10: of the order of 40 x 26 mm 2 dimensions of each of the slots 41 -44: of the order of
• the device 100 may have a mass which is less than or of the order of 70 kg, and dimensions which are less than or of the order of 900 mm ⁇ 620 mm ⁇ 450 mm, including a cryostat for contain the spectrophotometer but without counting a guard cylinder ("baffle" in English) that would be placed around the entrance E of the telescope 10.
• spectrophotometric measurements can be performed simultaneously in the four spectral bands to characterize carbon compounds that are contained in the Earth's atmosphere along the DP pointing direction.
• measurements which are carried out simultaneously measurements are meant whose simultaneity is limited only by the reading constraints of the pixels of the matrix detector 26.

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