RAPID: Evaluation of the Impact of Near-surface Turbulence on the Active Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS) Measurements

十多年来，首席研究员(PI)和他的团队一直在开发一种名为主动温度、臭氧和湿度微波光谱仪(ATOMMS)的大气遥感系统。ATOMMS结合了全球定位系统(GPS)无线电掩星(RO)和微波肢体探测仪(MLS)技术的最佳功能，通过无线电掩星(MLS的子集)主动探测MLS通过被动发射观测到的吸收线。对现有资料的分析表明，ATOMMS将在晴天和多云空气中以~200m的垂直分辨率将对流层、中层大气水汽和中层大气臭氧廓线降至1-5%，温度至0.5K，位势高度至10-20m。这一史无前例的表现将随着平均化而显著改善。由于掩星信号源是在每次掩星之前或之后立即观测到的，ATOMMS是自校准的，这消除了长期漂移。这些能力将满足气候变化监测、研究和政策制定的关键需求。这项研究集中在与ATOMMS开发相关的几个关键的近期研究目标上。该项目的目标是(1)完成即将完成的ATOMMS仪器的第一个版本，(2)在实验室完成仪器测试和性能评估，(3)首次使用该仪器测量近地表湍流对ATOMMS信号的影响，以及(4)根据最近的理论预测评估这种影响。即将完成的ATOMMS仪器的第一个版本提供了183 GHz附近的两个音调，这是进行有用的差分吸收测量所需的最低频率。简单地说，一个音调测量的是吸收加上由于天线指向等其他影响而产生的不必要的幅度变化，而第二个音调仅测量不需要的幅度变化。结果，两个色调的幅度之比在很大程度上消除了不需要的相对宽带的影响，如由折射率实部的湍流波动引起的影响，同时保留了大多数所需的气体吸收特征。该小组最近的一位博士发现了一个新的误差源：大气折射率虚部的湍流波动，它将产生与由于折射率实部波动而产生的显著幅度闪烁分开的现象。地面测量将首次测量由折射率实部和虚部的近地表湍流波动引起的ATOMMS信号闪烁(“恒星闪烁”)的大小，并提供分离和更好地理解这一新的误差源所需的关键信息。上述四个步骤对于ATOMMS遥感能力的全面评估和论证至关重要，必须在ATOMMS进入飞行测试和演示阶段之前完成，如果ATOMMS后续提案获得资金，该阶段将继续进行。即使ATOMMS后续提案没有得到资助，这些研究目标在科学上也是重要的，因为它们将确定新的RO气候仪器的性能并将其记录在同行评议的文献中，以及对ATOMMS气候监测系统的最终性能至关重要的不确定误差源。这个项目的智力价值是隔离和量化最近认识到的错误的关键来源。湍流测试将提供信息，以隔离、量化和减少由虚折射率和真实折射率的湍流波动引起的幅度闪烁。如果没有这些测量和后续分析，就不可能量化这一关键错误，从而导致对ATOMMS的评估不完整，其最终表现也不确定。长期目标是由十几个或更多的小型航天器组成的星座，进行ATOMMS掩星测量，提供密集的全球覆盖，完全穿透云层，并在每个轨道上进行白天采样。鉴于ATOMMS具有对气候特征至关重要的独特和强大的组合，它应该成为全球气候观测系统(GCOS)的关键要素，全球气候观测系统(GCOS)是解决气候变化问题的关键组成部分。

For more than ten years, the principal Investigator (PI) and his group have been developing an atmospheric remote sensing system called the Active Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS). ATOMMS combines the best features of the Global Positioning System (GPS) radio occultation (RO) and the Microwave Limb Sounder (MLS) techniques by actively probing via radio occultation (a subset of) the absorption lines that MLS observes via passive emission. Analyses of available data shows that ATOMMS will profile tropospheric and middle atmosphere water vapor and middle atmosphere ozone to 1-5%, temperature to 0.5K, and geopotential heights to 10-20 m, all with ~200 m vertical resolution, in both clear and cloudy air. This unprecedented performance will improve significantly with averaging. Because the occultation signal source is observed immediately before or after each occultation, ATOMMS is self-calibrating, which eliminates long-term drift. These capabilities will fulfill crucial needs for climate change monitoring, research and policymaking. This research focuses on several critical, near-term research objectives associated with the ATOMMS development. The objectives of this project are to (1) complete the nearly finished first version of the ATOMMS instrument, (2) complete the instrument testing and performance evaluation in the laboratory, (3) use the instrument to measure for the first time the impact of near-surface turbulence on the ATOMMS signals and (4) assess that impact against recent theoretical predictions. The nearly completed, first version of the ATOMMS instrument provides two tones near 183 GHz which is the minimum number needed to make useful differential absorption measurements. Simplistically, one tone measures absorption plus unwanted amplitude variations due to other effects such as antenna pointing and the 2nd tone measures just the unwanted amplitude variations. As a result, the ratio of the amplitudes of the two tones largely removes unwanted relatively broadband effects like those caused by turbulent fluctuations of the real part of the index of refraction while retaining most of the desired gaseous absorption signature. A recent Ph.D. in the group identified a new error source: turbulent fluctuations in the imaginary part of the atmospheric index of refraction that will produce significant amplitude scintillations separate from and in addition to those due to fluctuations in the real part of the refractivity. The ground measurements will for the first time measure the magnitude of the scintillations ("twinkling of a star") of the ATOMMS signals caused by near-surface turbulent fluctuations in the real and imaginary parts of the index of refraction and provide critical information needed to isolate and better understand this new source of error. The four steps summarized above are critical in the overall evaluation and demonstration of the ATOMMS remote sensing capability and must be completed prior to ATOMMS progressing to its flight testing and demonstration phase that will proceed if the ATOMMS follow-on proposal is funded. These research objectives are important and well-justified scientifically even if the ATOMMS follow-on proposal is not funded because they will determine and document in the peer-reviewed literature the performance of a new RO climate instrument and an uncertain error source critical to the ultimate performance of the ATOMMS climate monitoring system. The intellectual merit of this project is to isolate and quantify a recently recognized key source of error. The turbulence testing will provide the information to isolate, quantify and reduce amplitude scintillations due to turbulent fluctuations in the imaginary and real refractivity. Without these measurements and subsequent analysis, it will not be possible to quantify this critical error leaving the assessment of ATOMMS incomplete and its ultimate performance uncertain. The long term goal is a constellation of a dozen or more small spacecraft making ATOMMS occultation measurements which will provide dense, global coverage with complete cloud-penetration and diurnal sampling every orbit. Given its unique and powerful combination of qualities critical to characterizing climate, ATOMMS should be a key element in the global climate observing system Global Climate Observing System (GCOS) which is a crucial component in solving the climate change problem.