Wide Field Receiver Calibration Device for Micro Pulse LiDAR
Sensors
Wide Field Receiver Calibration Device for Micro Pulse LiDAR (GSC-TOPS-389)
Enhancing accuracy in atmospheric monitoring
Overview
Micro Pulse LiDAR (MPL) instruments – first developed in the early 1990s by a NASA scientist – are compact, eye-safe elastic-backscatter LiDARs deployable at remote locations. A federated ground network of MPLs compose the NASA MPL Network (MPLNET), which provides continuous aerosol and cloud profiling data around the globe. However, using MPLs – especially for aerosol research – in the near range (0-6 km) requires a time consuming, laborious overlap calibration process to quantify and correct the region where the emitted laser beam and detector field of view do not fully overlap. At close ranges, this overlap is often incomplete, leading to reduced signal accuracy. Accurate characterization and correction of this function are vital for precise data, especially for near-surface atmospheric features.
In response to this challenge, engineers at NASA's Goddard Space Flight Center developed the Wide Field Receiver (WFR) Calibration Device for MPLs. This auxiliary receiver has a broad field of view compared to the standard MPL receiver, allowing it to capture more scattered light from the atmosphere, including regions where the standard receiver’s overlap is complete. By comparing data from both standard and this NASA wide field of view receiver, users can accurately determine the overlap function and apply necessary corrections to MPL data, all with reduced time and effort relative to conventional techniques.
The Technology
Below an MPL’s minimum overlap range, the return signals are not completely in the instrument’s field of view, so the receiver only captures a portion of the backscatter laser pulse. MPL overlap ranges vary, but is usually between 4-8 km, encompassing the lower atmosphere where most aerosols reside. Commonly, correction entails recording horizontal profiles that require a ~10 km clear line-of-sight and homogenous atmospheric conditions, limiting the solution’s practicality.
In contrast, NASA’s WFR device corrects for the overlap using a second receiver co-aligned with the MPL that captures the same backscattered laser pulses as the MPL receiver, but with a ~20x wider FOV that enables a much shorter overlap range from ~6 km down to 250 m. Thus, the combination of the WFR and MPL can capture accurate signals from near surface to the stratosphere. The WFR utilizes the same detector as the MPL, enabling it to connect to the MPL data system for synced data acquisition. By eliminating the need for homogeneous horizontal measurements to determine the MPL overlap function, overlap corrections are more easily and more frequently obtained. Further, the WFR mount base was designed to easily integrate with MPLs.
NASA originally developed this device to improve accuracy of MPLs in the MPLNET, ensuring data collected are both accurate and reliable, thereby enhancing our understanding of atmospheric processes and contributing to more informed climate research and environmental modeling. The technology’s operational ease, flexibility, and cost savings are relevant to a wide range of scientific, environmental, and industrial applications. Companies that manufacture and sell MPLs may wish to offer this advanced calibration device as a product to enhance accuracy of MPL-based measurements. This NASA technology is at TRL 8 (Actual system completed and "flight qualified" through test and demonstration.) and is available for patent licensing.
Benefits
- Enhances MPL data accuracy: By addressing the overlap function – a critical factor in LiDAR data accuracy – NASA's MFR calibration device improves the accuracy of MPL-based atmospheric measurements. The device is particularly beneficial in environments with low planetary boundary layers, where standard MPL configurations might miss critical aerosol dynamics near the surface.
- Ease of integration: NASA’s WFR calibration device was designed to mate easily with existing MPLs. It also utilizes the same detector as MPLs, allowing it to be connected to the MPL data system for synced data acquisition.
- Calibration speed: Faster data analysis enables quicker turnaround of corrections and profiling.
- Increased uptime: Simplified, efficient overlap corrections allow more operation time to be allocated towards collecting new data.
Applications
- Atmospheric science & meteorology: cloud profiling, aerosol monitoring, boundary layer studies
- Environmental monitoring: air quality assessment, wildfire smoke and dust monitoring
- Remote sensing instrument validation & calibration: providing ground truth data for satellite instruments
- Aviation safety: determination of cloud base height, detection/tracking of volcanic ash or dust events for aviation hazard mitigation
- Urban & industrial monitoring: profiling emissions from industrial areas, monitoring regulatory compliance, environmental impact assessments
Technology Details
Sensors
GSC-TOPS-389
GSC-18641-1
“Investigation of Overlap Correction Techniques for the Micro-Pulse Lidar NETwork (MPLNET),” T.A. Berkoff, E.J. Welton, J.R. Campbell, V.S. Scott, and J.D. Spinhirne, January 1, 2003, https://ntrs.nasa.gov/citations/20040015235
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