RAPID: Low-cost, Lightweight Instrument for In Situ Measurements of Water Vapor on High-Altitude Balloons

该奖项支持开发用于热带对流层顶层(TTL)的湿度计或水蒸气传感器，TTL是对流层(云和降水的区域)和平流层(其上方包含臭氧层的寒冷和干燥区域)之间的过渡区。TTL水蒸气之所以引起人们的兴趣，有几个原因，包括它在卷云形成中的作用，卷云对地球的辐射能量平衡有很大的影响，以及平流层中的大部分水蒸气通过TTL进入。根据本奖项开发的湿度计旨在用于先前根据AGS-1643022开发的仪器组件RACHUTS，用于卷筒式气溶胶云湿度和温度传感器。RACHuTS是一个鞋盒大小的包裹，重量不到2公斤，通过一根2公里长的尼龙缆索连接到研究气球的吊篮上升降。RACHuTS旨在研究卷云的形成，收集温度、湿度和云粒观测，以观察由于环境空气过饱和而形成的卷云。湿度计取代了RACHuTS最初使用的Flash-B湿度计，后者已不再可用。对湿度计的要求相当具有挑战性，因为它必须测量百万分之2到500ppm的范围内的水蒸气，整个范围的分辨率低于5%，响应时间为1秒。它还必须在TTL环境中无人值守运行2-3个月。为了适合RACHuTS套装，它的重量必须小于700克，平均功耗不到3瓦。该项目开发的湿度计使用波长调制光谱来应对这些挑战，利用了为电信开发的分布式反馈红外激光器、开放式多程Herriott池以及面向爱好者销售的低成本微控制器。湿度计可以迅速发展，因为它类似于现有的湿度计，包括科罗拉多大学的第二代激光湿度计(CLH-2)。该项目包括在2023年发射的气球上进行试飞，湿度计应该及时可用于2024年部署的Strateole-2长时间气球运动。由于RACHuTS观测对于解决关于TTL过程的各种问题的价值，该工作具有更广泛的科学影响。此外，该奖项下的工作促进了一类新的低成本、轻量级仪器的开发，这些仪器可以用于各种配置和应用。潜在的应用包括从“飓风猎人”飞机上释放的专门的“投射探测仪”，以及用于公民科学的更小、更低灵敏度的版本。这一奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award supports development of a hygrometer, or water vapor sensor, for use in the tropical tropopause layer (TTL), the transition zone between the troposphere (the domain of clouds and precipitation) and the stratosphere (the cold and dry region above it which contains the ozone layer). TTL water vapor is of interest for several reasons including its role in the formation of cirrus clouds, which have a strong effect on earth's radiative energy balance, and the fact that much of the water vapor in the stratosphere enters through the TTL. The hygrometer developed under this award is intended for use in an instrument package previously developed under AGS-1643022 called RACHuTS, for Reel-down Aerosol Cloud Humidity and Temperature Sensor. RACHuTS is a shoebox-size package weighing less than 2kg which is raised and lowered on a 2km nylon cable attached to the gondola of a research balloon. RACHuTS is intended to study the formation of cirrus clouds, collecting the temperature, humidity, and cloud particle observations needed to observe the formation of cirrus clouds due to the supersaturation of ambient air. The hygrometer replaces the FLASH-B hygrometer originally used for RACHuTS, which is no longer available.The requirements for the hygrometer are quite challenging as it has to measure water vapor over a range of 2 to 500 parts per million with a resolution less than 5% over the whole range and a response time of one second. It also has to operate unattended in the TTL environment for 2-3 months. In order to fit the RACHuTS package it has to weigh less than 700 grams and have an average power consumption less than 3 watts. The hygrometer developed in this project uses wavelength modulation spectroscopy to meet these challenges, taking advantage of a distributed feedback infrared laser developed for telecommunications, an open multi-pass Herriott cell, and low-cost microcontrollers marketed to hobbiests. The hygrometer can be developed quickly because it is similar to existing hygrometers including the University of Colorado Second Generation Laser Hygrometer (CLH-2). The project includes a test flight on a balloon launched in 2023, and the hygrometer should be available in time for use in the 2024 deployment of the Strateole-2 long-duration ballooning campaign.The work has scientific broader impacts due to the value of RACHuTS observations for addressing a variety of questions regarding TTL processes. In addition, work under this award fosters the development of a new class of low-cost, lightweight instruments that can be used in a variety of configurations and applications. Potential applications include specialized "dropsondes" released from "hurricane hunter" aircraft and smaller, lower sensitivity versions for use in citizen science.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.