1. A dual-field multi-wavelength Raman lidar beam splitting system adapting to different cloud base heights is characterized by comprising a dual-field device, a large-field optical path system and a small-field optical path system, wherein the dual-field device comprises at least two dual-field beam splitters with different sizes so as to adapt to atmospheric detection of different cloud base heights; wherein the content of the first and second substances,

the double-view-field light splitting device is used for enabling one part of echo signals reflected by an atmosphere to enter the large-view-field light path system and the other part of the echo signals to enter the small-view-field light path system;

the large view field optical path system and the small view field optical path system are both used for screening optical signals with different wavelengths under corresponding view fields.

2. The dual-field multi-wavelength Raman lidar spectroscopy system adapted to different cloud base heights of claim 1, wherein the dual-field spectroscopy device comprises a large field portion and a small field portion, and the large field portion and the small field portion of each dual-field spectroscopy device are different in size.

3. The system according to claim 2, wherein the small field of view portion is used for transmitting small-angle scattered light in the echo signal, and the large field of view portion is used for reflecting large-angle scattered light in the echo signal.

4. The dual-field multi-wavelength Raman lidar spectroscopic system adapted to different cloud base heights of claim 1, wherein the dual-field apparatus further comprises a carrier, the at least two dual-field spectroscopic devices are disposed on the carrier, and the dual-field spectroscopic devices of different sizes are selected by moving the carrier.

5. The dual field multi-wavelength Raman lidar spectroscopy system of claim 4, wherein the carrier is a rotating disk and the at least two dual field spectroscopy devices are arranged along a circumference of the rotating disk.

6. The dual field multi-wavelength Raman lidar spectroscopy system of claim 4, wherein the carrier is a rectangular strip and the at least two dual field spectroscopy devices are arranged in a single row along a length of the rectangular strip.

7. The dual-field multi-wavelength Raman lidar spectroscopic system adapted to different cloud base heights of claim 1, wherein the small-field optical path system and the large-field optical path system have the same structure and each comprise a plurality of dichroic mirrors, filter mirror groups and photomultiplier tubes, and the filter mirror groups correspond to the photomultiplier tubes one by one; when the dichroic mirrors are multiple, different dichroic mirrors are plated with reflecting films aiming at different wavelength optical signals, the dichroic mirrors are sequentially arranged along the optical path, the optical signals transmitted by the dichroic mirrors in front of the optical path are input to the dichroic mirrors in rear of the optical path, the optical signals transmitted by the dichroic mirrors at the tail ends of the optical path are incident to the corresponding filtering mirror groups, and the optical signals reflected by the dichroic mirrors are incident to the corresponding filtering mirror groups and are absorbed by the corresponding photomultiplier tubes after being filtered by the filtering mirror groups.

8. The dual field-of-view, multi-wavelength raman lidar spectroscopy system of claim 7, wherein one set of filter lenses comprises a filter mirror and a lens, the lens being mounted optically behind the filter mirror.

Background

Aerosol-Cloud Interaction (ACI) is one of the most uncertain radiation forcing factors in the earth system, and is also one of the two main ways in which aerosols affect the radiation balance of the earth-atmosphere system. In the aerosol-cloud interaction, the aerosol has indirect influence on the climate by influencing parameters such as optical characteristics, cloud cover, water content, service life and the like of the cloud, wherein the indirect influence comprises a first type of indirect effect (Twyry effect) and a second type of indirect effect (Albercht effect or cloud life cycle effect); at the same time, the aerosol effect on the cloud also includes semi-direct effects. Therefore, the interaction of the aerosol and the cloud has extremely important influence on the atmospheric composition and global climate change, and the research on the interaction of the aerosol and the cloud has important scientific significance and research value on the influence and the action mechanism of atmospheric radiation balance and climate change.

Currently, researchers develop relevant researches on physical characteristics of aerosol and cloud micro by means of satellite, airborne, ground observation, numerical mode and the like. The airborne field observation technology has accurate measurement but high cost, is limited to case study, and is not suitable for long-time observation with statistical significance. The passive remote sensing measurement of the satellite can cover the global range, so that the observation can be carried out in a wide range for a long time, but the timeliness is poor. The lidar technology is an active remote sensing technology, and is commonly used in the fields of atmosphere, environment, weather, ocean and the like in recent years. In contrast, active remote sensing techniques, including lidar, allow long-term observations with high spatial and temporal resolution, and thus allow more in-depth studies of aerosol-cloud interactions. The cloud and aerosol characteristics are observed for a long time by utilizing active remote sensing, and both radar and laser radar technologies have feasibility. Compared with a laser radar, the penetration depth of the radar is wider, and the method has important significance for measuring the vertical cloud layer in a large range; but is not suitable for detection of thin cloud layers, water clouds, because the detection signal is below the radar detection threshold. In comparison, the laser radar is more suitable for being used as a detection tool for water cloud and aerosol. The laser radar can detect aerosol and cloud characteristic vertical distribution with high space-time resolution, so the laser radar becomes an important means for researching the aerosol and cloud characteristics. The lidar has higher sensitivity to smaller droplets which are the main component in the atmospheric environment, and therefore can detect the formation of droplets and the cloud bottom area mixed with aerosol particles with high precision.

In conclusion, the detection research of the aerosol-cloud interaction by using the laser radar has good application prospect and realizability. However, no corresponding system exists at home at present, and the laser radar system for foreign detection of water cloud has a complex structure, needs multiple instruments and equipment to be matched with each other for use, is complex to operate and is not suitable for popularization and application.

Disclosure of Invention

The invention aims to provide a double-field-of-view multi-wavelength Raman laser radar light splitting system suitable for different cloud base heights, which is applied to a laser radar system for water cloud detection so as to simplify the structure of the laser radar system.

In order to achieve the above object, the embodiments of the present invention provide the following technical solutions:

the embodiment of the invention provides a dual-field multi-wavelength Raman lidar beam splitting system suitable for different cloud base heights, which comprises a dual-field device, a large-field optical path system and a small-field optical path system, wherein the dual-field device comprises at least two dual-field beam splitting devices with different sizes so as to be suitable for atmospheric detection of different cloud base heights; wherein the content of the first and second substances,

the double-view-field light splitting device is used for enabling one part of echo signals reflected by an atmosphere to enter the large-view-field light path system and the other part of the echo signals to enter the small-view-field light path system;

the large view field optical path system and the small view field optical path system are both used for screening optical signals with different wavelengths under corresponding view fields.

In the scheme, the double-view-field device is utilized, so that the scattered light with different angles respectively enters different view fields, light splitting with different scattering angles is realized, optical signals with different wavelengths can be screened out by the large/small view field optical path system, and screening of different wavelengths is realized. The whole system not only can realize multi-wavelength double-field light splitting, but also has simple structure, and when the system is applied to a laser radar system, the structure of the whole laser radar system can be simplified. In addition, by arranging at least two double-view-field light splitting devices with different sizes, the atmospheric detection requirements of different cloud base heights can be met under the condition that an optical path system is not changed, the structure of the whole system is further simplified, and the operation is simpler. That is, the technical problem of how to detect water clouds of different heights without changing the optical path can be solved.

In the scheme of the invention, the dual-field light splitting device comprises a large field part and a small field part, and the sizes of the large field part and the small field part of each dual-field light splitting device are different.

In the scheme, the large view field part and the small view field part of each double-view-field light splitting device are different in size, so that the double-view-field light splitting device can be better suitable for water detection at different cloud base heights.

In one possible embodiment, the small field of view portion is used to transmit small angle scattered light in the echo signal and the large field of view portion is used to reflect large angle scattered light in the echo signal.

In the scheme, the optical signals of the small visual field and the large visual field are distinguished in the transmission and reflection modes respectively, the implementation mode is simple, and the complexity of the system can be reduced.

In one embodiment, the dual-field-of-view apparatus further includes a carrier, the at least two dual-field-of-view beam splitters are disposed on the carrier, and the dual-field-of-view beam splitters of different sizes are selected by moving the carrier.

In the above scheme, through removing the mode that the carrier realizes chooseing for use of the double-view-field light splitting device of not unidimensional compares in the mode of changing (that is to say pulling down original double-view-field light splitting device and installing the double-view-field light splitting device of other sizes) double-view-field light splitting device, and the operation is simpler, convenient, has still realized double-view-field light splitting device's installation fixed with the help of the carrier simultaneously.

In one possible embodiment, the carrier is a rotating disk and the at least two dual field of view beam splitters are arranged along a circumference of the rotating disk. The carrier is a rectangular belt, and the at least two double-view-field light splitting devices are arranged in a single row along the length direction of the rectangular belt.

When the carrier is a turntable, the dual-field light splitting devices with different sizes can be selected by rotating the turntable; when the carrier is a rectangular belt, the double-view-field light splitting devices with different sizes can be selected by dragging the rectangular belt, the implementation mode is simple, and the operation is convenient.

In one possible embodiment, the large-field optical path system and the small-field optical path system have the same structure and each include a plurality of dichroic mirrors, filter lens groups and photomultiplier tubes, and the filter lens groups correspond to the photomultiplier tubes one by one; when the dichroic mirrors are multiple, different dichroic mirrors are plated with reflecting films aiming at different wavelength optical signals, the dichroic mirrors are sequentially arranged along the optical path, the optical signals transmitted by the dichroic mirrors in front of the optical path are input to the dichroic mirrors in rear of the optical path, the optical signals transmitted by the dichroic mirrors at the tail ends of the optical path are incident to the corresponding filtering mirror groups, and the optical signals reflected by the dichroic mirrors are incident to the corresponding filtering mirror groups and are absorbed by the corresponding photomultiplier tubes after being filtered by the filtering mirror groups.

Compared with the prior art, the light splitting system has the advantages that the whole system can realize multi-wavelength double-view-field light splitting, the system structure is simple, and when the light splitting system is applied to a laser radar system, the structure of the whole laser radar system can be simplified.

Other advantages of the invention will be apparent from the detailed description which follows.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

Fig. 1 is an optical path diagram of a dual-field multi-wavelength raman lidar spectroscopic system adapted to different cloud base heights in an example of an embodiment.

Fig. 2 is a schematic structural diagram of the dual-field device in the embodiment.

Fig. 3 is another structural schematic diagram of the dual-field device in the embodiment.

Fig. 4 is a light path diagram of the laser radar system in the embodiment.

FIG. 5 is a graph of measured water cloud extinction coefficient versus height.

FIG. 6 is a graph of measured effective particle radius of a water cloud versus liquid water content.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment provides a dual-field multi-wavelength Raman lidar beam splitting system suitable for different cloud base heights, which comprises a dual-field device, a large-field optical path system and a small-field optical path system. The double-view-field device is mainly used for enabling one part of echo signals reflected by an atmosphere to enter a large-view-field optical path system and the other part of echo signals to enter a small-view-field optical path system; the large-view-field optical path system and the small-view-field optical path system are used for screening optical signals with different wavelengths under corresponding view fields.

Referring to fig. 2 and 3, in the present embodiment, the dual field device includes a carrier and 3 dual field beam splitters, and the 3 dual field beam splitters are disposed on the carrier. In the structure shown in fig. 2, the carrier is a turntable, and 3 dual-field beam splitters are arranged along the circumference of the turntable. In the structure shown in fig. 3, the carrier is a rectangular strip, and 3 dual-field beam splitters are arranged in a single row along the length direction of the rectangular strip.

The double-view-field light splitting device comprises a large view field part and a small view field part, wherein the small view field part is used for transmitting small-angle scattered light in echo signals, and the large view field part is used for reflecting large-angle scattered light in the echo signals. When the dual-field beam splitter is two or more, the sizes of the large field part and the small field part of each dual-field beam splitter are different. For example, in the structures shown in fig. 2 and 3, the sizes of the large field portions of the 3 dual-field spectroscopy devices are different, and the sizes of the small field portions of the 3 dual-field spectroscopy devices are also different.

In one embodiment, the dual-field beam splitter is a lens with a light hole in the center, the light hole is the small field of view portion, the lens is coated with an annular (not necessarily circular, but also elliptical or square) reflective film, the reflective film is the large field of view portion, and the large field of view portion is at the periphery of the small field of view portion. For the case of a circular light hole and a circular ring-shaped reflective film, the size of the small field of view portion of the dual field of view splitter refers to the diameter (or radius) of the light hole, and the size of the large field of view portion refers to the diameters (or radii) of the inner ring and the outer ring of the reflective film.

In this implementation, the purpose of arranging a plurality of double-view field light splitting devices on a carrier is to select the double-view field light splitting devices with different sizes according to different requirements, so as to realize the detection of water clouds with different heights without changing the light path, thereby not only enhancing the applicability of the system, but also reducing the complexity of the system.

It is easily understood that, in other embodiments, the dual-field spectroscopy device may not need a carrier, and the dual-field spectroscopy device is installed in a detachable connection manner, so as to replace the dual-field spectroscopy device with different sizes. It is also easy to understand that the structure of the carrier may adopt other ways based on different implementations, and is not limited to the structures shown in fig. 2 and fig. 3, and the number of the dual-field spectroscopy devices arranged in the carrier is not limited.

Scattering from larger diameter particles will result in a smaller forward scattering angle, and scattering from smaller diameter particles will result in a larger forward scattering angle. According to the relation between the particle size and the generated scattering angle, the scattering light of the echo signal reflected by the atmosphere can be divided into a large-angle scattering light and a small-angle scattering light; the large-angle scattered light enters the large-view-field optical path system, the small-angle scattered light enters the small-view-field optical path system, and the rest interference light beams which do not belong to the scattered light are completely shielded in the large view field and the part of the double-view-field light splitting device. It will be readily understood that the large and small angle scattered light described herein, or the large and small in the large and small field of view optical path systems, are relative concepts and there is no absolute angular limitation.

Referring to fig. 1, the small field optical path system includes a plurality of dichroic mirrors (BS), a plurality of filter mirror sets (IF + L), and a plurality of photomultiplier tubes (PMT), the filter mirror sets and the photomultiplier tubes are in one-to-one correspondence, that is, one dichroic mirror corresponds to one filter mirror set, and one filter mirror set corresponds to one photomultiplier tube, and each photomultiplier tube is powered by a negative high voltage power supply (-HV). The number of the dichroic mirrors is one less than that of the filter mirror groups, the number of the filter mirror groups is determined by the number of the wavelengths of the light, and the light with one wavelength corresponds to one filter mirror group. In this embodiment, one filter lens group includes one filter lens and one lens, and the lens is installed behind the optical path of the filter lens.

In the structure shown in fig. 1, 3 dichroic mirrors, which are BS1, BS2, and BS3, are arranged in sequence along the optical path, and each dichroic mirror is coated with a reflective film having high reflectivity for light of different wavelengths, respectively, to reflect the light of different wavelengths out. For example, the small-angle scattered light passing through the light hole is firstly incident to the BS1, and the BS1 reflects the light with the wavelength of 355nm to a corresponding filter set (IF2+ L2), and the light is filtered by the filter set and then absorbed by a corresponding photomultiplier tube (PMT 3). Optical signals with other wavelengths are transmitted out of the BS1 and enter the BS2, the BS2 reflects optical signals with 532nm wavelength, transmits optical signals with other wavelengths and enters the BS3, the BS3 reflects optical signals with 607nm wavelength and transmits optical signals with other wavelengths, and optical signals with 660nm wavelength are transmitted by the BS3 and then enter the corresponding filter mirror group (IF5+ L5).

The structure of the large-view-field optical path system is similar to that of the small-view-field optical path system, and the large-view-field optical path system also comprises a dichroic mirror (BS), a filter mirror group (IF + L) and photomultiplier tubes (PMT), wherein the filter mirror group and the photomultiplier tubes are in one-to-one correspondence, and each photomultiplier tube is powered by a negative high-voltage power supply (-HV). In the structure shown in fig. 1, a dichroic mirror is one, and a reflective film with high reflectivity is plated for an optical signal with a wavelength of 607nm, the optical signal with the wavelength of 607nm is reflected by BS0, enters a corresponding filter set (IF1+ L1), is filtered by the filter set, and is absorbed by a corresponding photomultiplier tube (PMT2), and the absorbed optical signal is transmitted to a data acquisition system by the photomultiplier tube and is converted into an electrical signal by the data acquisition system. The 532nm wavelength optical signal is transmitted by BS0, enters a corresponding filter set (IF0+ L0), and is absorbed by a corresponding photomultiplier tube (PMT1) after being filtered by the filter set.

Referring to fig. 4, the optical splitting system shown in fig. 1 is applied to a laser radar system for atmospheric detection. The Laser radar System also comprises a Laser (Nd: YAG Laser), a telescope (telescope) and a data acquisition System (DAQ System).

Wherein the laser is used for emitting laser beams to the atmosphere. When the system is arranged, the laser beam emitted by the laser can be directly incident to the atmosphere; as shown in fig. 4, the light may be reflected by a mirror and then incident into the atmosphere.

The telescope is used for receiving echo signals in the atmosphere. After the laser signal is transmitted to the atmosphere, the laser signal is reflected by the atmosphere to form an echo signal which can be received by a telescope. In the experiment, the telescope is a Cassegrain telescope. According to the layout requirement, the echo signal output by the telescope can be directly incident to the double-view-field light splitting device; as shown in fig. 4, the light may be reflected by the total reflection mirror (M1) and then incident on the dual field of view beam splitter. In the system, if the output end of the telescope and the input end of the dual-field-of-view beam splitter are arranged at 90 degrees, the total reflection mirror is preferably arranged at an angle of 45 degrees, so that echo signals reflected by the total reflection mirror can be incident to the dual-field-of-view beam splitter in parallel.

The large-angle scattered light and the small-angle scattered light enter the data acquisition system after being processed by the large-view-field optical path system and the small-view-field optical path system respectively, and are converted into electric signals for inversion by the data acquisition system.

The choice of field angle typically maximizes the received scatter contribution, so the field angle choice for dual fields of view is also based on this view. The hardware conditions of the optical observation base of northern national university in Yinchuan city are as follows: the laser beam divergence γ s is 0.15mrad, the cassegrain telescope receiving aperture Dr is 406.4mm, and the laser beam diameter Ds is 9 mm. Defining the field angles of the double fields of view as a small field angle gamma in and a large field angle gamma out respectively; the field angle of the dual field is determined by the cloud base height H, the depth z of detection of the cloud, the telescope receiving aperture Dr and the laser beam diameter Ds.

Among them, Dr/H can be approximated as the best field angle estimate for extinction measurement, for large field angle γ out: and gamma _ out is 0.01 z/H.

The parameter of the double-field light splitting device is drawn up as shown in the following table:

the small field of view in the above table refers to the scattering angle of the light-transmitting hole, the large field of view refers to the scattering angle of the reflection film region on the lens, mrad is the unit of milliradian, and the mrad can be converted with the mrad, and is generally used for representing the range of the lens which can receive light. The large field diameter in the above table means the diameter from the center of the lens to the portion coated with the reflective film, and the small field diameter means the diameter of the light-transmitting hole.

In the measurement process of the double-view-field light splitting device, the double-view-field light splitting devices with different sizes are carried in the light path to realize the control of the sizes of the large view field and the small view field, so that the large view field angle and the small view field angle are controlled to change correspondingly; by the method, the water cloud measurement process with different cloud bottom heights can be adapted, so that more and more comprehensive measurement data information can be obtained.

For the detection of water cloud, the laser radar echo signal mainly depends on the detection depth of the cloud and the size of the field angle, and the detection depth Z of the cloud is generally determined by the speed of light c, the time t when a photon reaches a detection point, and the height H of the cloud bottom.

For the nitrogen raman scattering process, the lidar equation for the nitrogen vibration raman echo signal is:

wherein Q is the absolute calibration constant of the multi-wavelength laser radar detection system, PN (z) is a nitrogen vibration Raman backscattering signal, and beta_NIs the nitrogen molecule vibration Raman backscattering coefficient, beta_NEqual to the product of the number density of nitrogen molecules and its raman backscattering cross-section. Alpha represents the extinction coefficient, lambda represents the laser wavelength, lambda₀Is the laser emission wavelength, λ_NIs the nitrogen molecule scattering wavelength.

The water cloud and the fog in the atmosphere can be described by popularizing the cloud function, the model can well reflect some distribution characteristics of the cloud in the low altitude, and the cloud volume concentration distribution function is as follows:

n(r)＝2.373r⁶e^-1.5rcm^-3μ^-1wherein n (r) is the volume concentration at the radius r, and the cloud particle volume concentration reaches the peak value about 3-6 μm for the low-altitude water cloud, which provides a theoretical basis for the inversion of the effective radius of the water cloud particles.

For the water cloud with the cloud bottom height of 1.5km-5km, the influence of multiple scattering on echo signals must be considered in the scattering process, in order to research the properties of the water cloud, a multiple scattering model proposed by Luc R.Bissonnette et al is adopted to invert the effective particle radius of the water cloud, and the multiple scattering laser radar echo equation is as follows:

P(z，θ)＝P_ss(z)M(z，θ)

where P (z, theta) is the received multiple scattering lidar return power, P_ss(z) is the single-scattering lidar equation, and M (z, θ) is a multiple-scattering correction factor, which can be divided into F_d(diffraction component part) and F_g(all other scattering involving at least one geometrical optical scattering).

For cloud particles with visible and near-infrared wavelengths, the maximum field-of-view return signal and the minimum field-of-view return signal are used in multi-field-of-view measurement to calculate the optical thickness of the water cloud, and the research according to bisson net et al includes:

wherein delta_dIs a relative multiple to single scattering backscattering coefficient, is generally equal to 0.7 in visible and near infrared wavelength water clouds, and τ (z) represents the optical thickness and can be associated with the multi-field lidar return signal equation P (z, θ), where θ is_maxAnd theta_minThe echo signals of the maximum field of view and the minimum field of view measurements, respectively.

According to the Luc R. Bissonnette et al study, a fitting parameter θ was defined_mdProportionality constant k, correlation function f (z), effective particle diameter d for water cloud_eThe following calculation formula is provided:

wherein z is the detection height, z_jλ is the lidar wavelength, which is the height of the boundary between two scattering media, e.g. the height of the boundary between the atmosphere and the water cloud. About fitting parameter θ_mdThe determination and evaluation of the proportionality constant k and the correlation function f (z) can be referred to the research of Luc r.

For water clouds, Liquid Water Content (LWC) is another important micro-physical property, for which ω L:

in the formula, rho is 1g/cm ^3, which is the liquid water density, re is the effective liquid drop radius, and for the water cloud measurement process, the rho is the effective radius of the water cloud particles; according to the study of c.jimenez et al, cloud extinction can be approximated by an extinction efficiency factor Qext (x, m) for the calculation of liquid water content. The extinction efficiency factor Qext (x, m) depends on the particle size parameter x and the complex refractive index m of the cloud particles relative to the surrounding medium, and the complex refractive index m is approximately 1.33 for the water cloud measurement process; in actual measurement the cloud particle effective radius is much larger than the laser wavelength, so the approximate Qext ≈ 2. Substituting into cloud particle size distribution n (r), the liquid water content ω L has the following expression

Based on the formula, according to actually measured data of the multi-wavelength dual-field-of-view laser radar, inversion of atmospheric parameters of water cloud and aerosol can be carried out, wherein the atmospheric parameters comprise extinction coefficient, backscattering coefficient, optical thickness, effective particle radius of the water cloud, liquid water content and the like.

By using the laser radar system shown in fig. 4, the laser radar echo signals and time at the height corresponding to the two fields of view can be measured, and the parameters can be inverted according to the measurement results. As shown in fig. 5 and fig. 6, there are respectively a water cloud extinction coefficient and height map, a water cloud effective particle radius and liquid water content map obtained by inversion from actual measurement data.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.