Through the 2017 Decadal Survey and subsequent PBL study team reports, the NASA Decadal Survey Incubation (DSI) program is prioritizing the need for improved PBL observations for Earth Science and societal benefit and recommend a decadal path of ‘PBL incubation’ towards a future spaceborne mission. To address this need, community led ESTO/DSI funded projects are underway to mature PBL technology, retrieval algorithms, and modeling capabilities. Critical uncertainties and knowledge gaps remain, associated with the PBL thermodynamics (i.e., temperature and water vapor profiles), PBL evolution and dynamics (e.g., PBL height, wind), measurement accuracy and the key processes and scales necessary for fully characterizing the PBL. It is recognized that no single sensor can achieve these observations at the necessary accuracy and scales for transformative PBL science applications. Rather, a dedicated PBL NOS with a ‘system of systems’ approach, that leverages spaceborne, airborne, and ground-based technology, models, and observations is needed to provide a comprehensive global and routine monitoring of the PBL and its complex processes and evolution. In preparation for this grand challenge, WHyMSIE (Westcoast & Heartland Hyperspectral Microwave Sensor Intensive Experiment) is the very first step forward towards an integrated, intelligent, and affordable PBL observing system of systems. It will bring together multiple observing nodes – i.e., space, suborbital, and ground – from passive and active sensors to enable a comprehensive and coherent picture of essential PBL thermodynamic variables such as temperature, water vapor, height, and hydrometeors to provide new understanding of the PBL that is not possible with any single sensor, observational approach, or scale. Through a partnership between NASA and NOAA, this field campaign will demonstrate the first-of-its-kind hyperspectral microwave airborne measurements (CoSMIR-H) and will be complemented by other passive (infrared, visible) and active (lidar) sensors onboard the NASA ER-2 aircraft. Serving as a future NASA planetary boundary-layer (PBL) mission prototype, WHyMSIE aims to capture a wide variety of thermodynamic, moisture, and PBL regimes across a variety of surface types. The ER-2 will be flying over a variety of land and ocean environments. Over land, the aircraft will maximize validation opportunities by overflying radiosonde launch sites as well as locations with PBL relevant ground-based in situ and remote sensing measurements. We will overflying the ARM Southern Great Plains (SGP) Central Facility (CF) with high frequency ensure maximum scientific value for understanding and validating the retrieved temperature and water vapor profiles from the WHyMSIE instrument payload. Over water, we aim to capture a wide range of temperature and water vapor conditions, with a specific focus on clear sky scenes for high quality comparisons with program of record (POR) satellite instruments (e.g. ATMS, AMSU). Comparing hyperspectral microwave retrievals from CoSMIR-H with in situ temperature and humidity information will allow for scientific advancement of remote-sensing techniques into the hyperspectral microwave era and improved understanding of the PBL at different measurement scales. WHyMSIE’s Payload WHyMSIE payload collects a total of eight instruments, as described in Table 1. The spatial resolution specifications reported in the table are referred to the ER-2 aircraft which will fly at an altitude of 20km. WHyMSIE will occur during two weeks in July 2024, to execute engineering test flights of CoSMIR-H and MBARS. Four additional weeks of flight will occur in October and November 2024 using the complete payload deployment. Conceived as a companion experiment for validation of WHyMSIE, the Active and Passive Profiling EXperiment (APEX) will deploy the High Altitude Lidar Observatory (HALO) on board of the G-III aircraft and the Aerosol Doppler Wind Lidar (AWP) as a piggy-back instrument for additional contextual information on wind fields. HALO will provide vertical profiles of water vapor, aerosol and cloud optical properties at a data rate of 2 Hz. HALO has a nominal spatial resolution of 6-12 km horizontally and 315 m vertically at an altitude of 10-12 km. The GIII will under-fly the ER-2 in different PBL regimes to evaluate information content of different sensors and develop an ideal dataset to enable active/passive retrievals of water vapor and temperature profiles and improved quantification of PBL heights. Table 1. WH2yMSIE and APEX (denoted by *) payloads provide a comprehensive, multi-sensor airborne experiment, embracing passive and active sensors from the Program of Record (POR) along with novel technology funded through the FY21 NASA ESTO PBL DSI and Instrument Incubation Programs. Altogether, this payload provides a first-of-a-kind PBL sensor architecture prototype, acting as a testbed for technology and retrieval concepts. *Flying on the NASA G-III Instrument Description Measurement Type ER2 based Spatial Scale Conical Scanning Millimeter-wave Imaging Radiometer - Hyperspectral (CoSMIR-H) Vertical profiles of temperature, water vapor and cloud properties Hyperspectral Microwave 1 km Microwave Barometric Radar and Sounder (MBARS) Surface pressure measurements Doppler Radar 1-4 km Cloud Radar System (CRS) High-resolution profiles of reflectivity and Doppler velocity in clouds Doppler Radar 300 m Cloud Physics Lidar (CPL) Cloud optical depth, cloud layer boundaries, and PBL height Backscatter Lidar 125 m Scanning-High-resolution Interferometer Sounder (S-HIS) Vertical profiles of temperature, water vapor Infrared 3 km National Airborne Sounder Testbed - Interferometer (NAST-I) Vertical profiles of temperature, water vapor Infrared 2.5 km Advanced Microwave precipitation Radiometer (AMPR) Cloud, precipitation, water vapor, and surface properties (including ocean winds) Microwave 0.64 km - 2.78 km MODIS-ASTER Airborne Simulator (MASTER) Cloud properties, aerosol and surface properties Visible-Infrared 50 m Airborne Radio Occultation (ARO) Vertical profiles of temperature and water vapor GPS Radio Occultation High Altitude Lidar Observatory (HALO)* Vertical profiles of water vapor, aerosol, and cloud optical properties Differential Absorption Lidar 6-12 km x 315 m Aerosol Doppler Wind Lidar (AWP)* Winds from aerosol Doppler shift Doppler Lidar ~ 2 km Dropsondes* Vertical profiles of temperature, water vapor, and winds In Situ N/A Partners: