Wide-Field Receiver (WFR)-
Our WFR is a solution to an issue present in all lidar systems; the "overlap" between the transmit and receive paths. Because of spatial separation (in biaxial setups) or differences in receiver field-of-view and transmitter divergence (in coaxial setups), a correction is needed for any backscattered light within this overlap regime. Typically this correction is done before the instrument is deployed, but this requires a trusted local calibration instrument and enough spacing between the two to prevent crosstalk. This method of calibration can sometimes take several weeks to wait for suitable weather and can introduce delays in other instruments bound for the field, so a solution was developed that offers the user a full-time, on-site overlap calibration of fielded instruments - specifically the Micropulse Lidar (MPL) and it's overlap of ~6km. This technology was designed in collaboration with NASA Goddard Space Flight Center. Download the concept sheet here.
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The WFR utilizes the central obscuration of the MPLs Maksutov-Cassegrain telescope and provides a second wide FOV receiver in the shadow of the MPL beam, sending the received light to an external detector and a coincident data input. Radially distributed fine-threaded adjusters provide the user boresight capabilities with an precision of ~0.005Ëš The WFR is polarization insensitive and can fully sample the MPL beam at a range of ~200m and has enough SNR to exceed the overlap range of the MPL during nighttime observations. By collecting both the inherent MPL signal and the external WFR channel together, the user can compare the two normalized signals to deduce the scaler overlap calibration.
Embedded within the controller for the WFR is a Single Photon Counting Module (SPCM), optical bandpass filters, and an internal shutter with flexible user I/O. The SPCM and it's dynamic range provide ample SNR but is susceptible to damage from noontime sun because of the wide FOV of the instrument, so we incorporate an internal shutter that automatically closes - the same controller that was developed for our Iris Family. Our WFR mates with the Full-Sized Iris for those sites that dictate the use of both.
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Optical Specifications -
• ø50mm center-mounted receiver.
• Polarization insensitive for use with PMPLs.
• 1.4mRad field-of-view.
• 0.15nm FWHM spectral filtering
• ~0.005Ëš boresight accuracy.
• Internal automatic shutter for sun protection.
• Fiber-coupled connection to external SPCM.
• Optional interface with MPL Iris System.
• Max range(1) 16km (nighttime), 4km (daytime).
• MPLNET approved design.
• Swappable between MPL systems.(2)
(1) Max range strongly dependent on MPL output energy and C-Value. Typical values given.
(2) WFR system may be swapped between MPLs but requires a boresight alignment each time.