The outfitting of the P-3 included:

• Physical transfer and installation of ELDORA from the Electra to the P-3;
• Installation of the French Leandre II Water Vapor Differential Absorption Lidar (DIAL) including the design and construction of a window fairing;
• Development of the "Pip Squeak" eye-safe radar;
• Outfitting of the aircraft interior with instrumentation racks, data and communications system;
• Installation of supporting meteorological sensors including the Tunable Diode Laser (TDL).

The ELDORA radome installed on the NRL P-3 at the Research Aviation Facility hangar. The radome antenna is being mated to the trail of the P-3. The rest of the ELDORA equipment was installed in racks inside the cabin.

The transfer of ELDORA and the installation of other IHOP instrumentation was complicated by a Navy requirement that all equipment be 20 G compliant. As a consequence, the electronics for ELDORA, the Aircraft Data System (ADS), the Weater Avoidance Radar (WARDS) and the French DIAL had to be repackaged and fit into specially- designed racks built by a Navy contractor and ATD's Design and Fabrication Services. The repackaging also required major rewiring within the aircraft.

Floor modifications: vecause the equipment required for IHOP exceeded the allowable floor load limits of the aircraft, major modifications were needed to strengthen the P-3 floor and the weight had to be redistributed. The solution suggested by NADEP would have delayed the departure of the P-3 into the field by almost three weeks. So the engineering staff of ATD produced the design and analysis for an alternative, easier solution and also constructed the new floor, resulting in only a minor delay in deployment. An example of an engineering analysis carried out during this modification is shown in the picture below.

Finite element analysis of the P-3 for determination of its load carrying capacity.

Leandre II: Early in the planning process, IHOP scientists identified the CNRS Leandre II differential absorption lidar (DIAL) as one of the most important airborne instruments beeded to achieve the scientific goals set for the program. Although Leandre is an airborne lidar and routinely flies on a French aircraft, it had never been flown on a US aircraft before. Parts of the instrument had to be reconfigured and put into racks, and the electronics had to be redistributed so that some parts could be installed under the floor. As a result, major rewiring was needed and all cables had to be replaced. ATD worked with the French group from CNRS to install the lidar on the P-3.

Window Fairing: The IHOP PIs needed Leandre to operate in not only a downward- but also a sideward-looking mode. This unique configuration provided for the first ever quality horizontal cross-sections of water vapor in regions where sharp moisture gradients were present. IHOP investigators decided to combine the sideward-looking Leandre data with ELDORA winds data to attempt improved understanding and predictions of the onset of convective storms. Because the aircraft has no downward-looking optical port, it was necessary to design and construct a window fairing with a turning mirror, all of which was designed, built and installed by ATD's Design and Fabrication Services with help from Performance Composites. The fairing also contained the antenna for a lightweight 25 KW pulsed, X-band radar affectionately termed "Pip Squeak" for potential airborne hazard identification and Lidar laser shutdown. The radar design, which consists of this special antenna, coherent processing, and a standard transmit-receive unit, performed flawlessly and provided a level of safety in airborne laser operations thought by some to be impossible.

Redesign of Scientist Station and Communications: Modifications also had to be made to the aircraft mission scientist area. A flat panel monitor was mounted to the table to display ELDORA data. An improved communications system that simplified aircraft-to-aircraft and aircraft-to-ground communications was accomplished when NCAR installed radio and satellite communications equipment in the forward navigator seating area. Not satisfied with the current set of tools available for mission scientists to direct and modify sampling strategies, a real-time flight level constant altitude PPI (CAPPI) display capability was also added to ELDORA.

State Parameters: Due to time constraints, only the most important state parameters measuring instruments were installed on the NRL P-3. These included two unheated Rosemount temperature probes, one heated pitot, two static ports, a GPS, a hygrometer, pressure transducers, an Inertial Reference System and a TDL laser hygrometer (shown to the left). Modifications had to be made to the radome air motion sensing system and a C-Band radar was installed in the nose of the airplane.

Certifications: Before the airplane left for Oklahoma City, the entire payload had to be approved and certified by the Naval FAA-equivalent, the Naval Air Systems Command (NAVAIR). Approval from a local NAVAIR inspector was needed for the gust probe holes, the TDL hygrometer, a UHF Freewave radio, the flat panel monitor display in the scientist area, the Satcom and the VHF radio. NAVAIR also reviewed all drawings, data and analyses, and physically inspected and signed off on all structural, electrical and aerodynamic modifications related to the ELDORA rotodome, Leandre fairing, Leandre and the ELDORA equipment racks. Last, an EMC test of ELDORA, Leandre, the eye-safety radar and WARDS had to be conducted before final clearance was issued.

DFS, RAF and NRL folks anxiously awaiting the outcome of the first P-3 test flight after all installations were completed.

3. The IHOP Field Project

Heavy rain depends on an ample supply of moisture, so the lack of water-vapor data is a major impediment to good forecasts. Currently, no device can track water vapor over large areas. Radiosondes provide most of the water-vapor data used in forecasting; however, their high cost reduces the frequency and spacing of balloon launches. Lidars provides more detail than radiosondes, but they can only sample across a few miles, and clouds limit measurements. Satellite sensors, which cover much of the globe, haven't yet furnished the high-resolution measurements needed in the lower atmosphere for storm prediction.

With a unique mix of older and newer sensors from the US and Europe, the IHOP scientists examined how the latest technology can bridge the gaps in water-vapor sensing. More than 50 airborne and groundbased instrument platforms were deployed near either Liberal, KS or Oklahoma City, OK to collect datasets in support of IHOP objectives. Four out of the six IHOP aircraft carried state-of-the-art remote sensing systems, including passive and microwave sounders and differential absorption lidars. Other systems include radiometers that profile temperature, humidity, and cloud liquid by sensing tiny amounts of molecular radiation. NCAR's S-Pol radar assessed the atmosphere's refractivity, allowing identification of horizontal transitions in moisture content. Sensors on the ground used signals from the Global Positioning System (GPS) to make slant-path measurements. The IHOP aircraft and ground-based mobile units monitored conditions in and near atmospheric boundaries, including the recurrent dry line, a frontal feature that often serves as a focus for spring storms. Wind data from profilers already in place across the network were joined by special radiosonde launches called reference radiosondes, and a variety of fixed measurement platforms were added for the experiment, including soil moisture stations.

A strong modeling and nowcasting element was part of IHOP. Investigators were collocated with operational forecasters from NOAA's Storm Prediction Center; they examined a suite of models run in near-real time using a subset of readily-available data.

In summary, more than 50 instruments were deployed, approximately 2500 more sondes than usual were launched and a total of 36 Intensive Observing Periods were conducted. Scientists collected 268 hours of airborne water vapor lidar measurements and 76 hours of satellite evaluation measurements. And last, IHOP even had its own satellite, GOES-11, which provided data exlusively for IHOP.

4. IHOP Data

Improvements in Nowcasting Convective Activity

The radar refractivity technique was initially proposed by Professor Frederic Fabry of McGill University and NCAR collaborators, while Fabry was an Advanced Study Program Fellow at NCAR/ATD. The technique relies upon the change in the measured speed of radar signals and on changes in the refractive index of the air. The time of arrival of the radar signal between fixed ground clutter signals provides maps of refractive index. Data Image 2 provides a refractive index map that corresponds to the radar reflectivity map shown in Data Image 1. Note that the arrows depicting radar fine lines correspond to gradients in the refractive index. The reddish colors are indicative of warm and dry air, while the green colors indicate moist and cool air.

Other examples are shown in Data Image 3 which depicts the evolution of a phenomenon called a dryline. Drylines mark a sharp mositure gradient where storms often form and the radar refractivity pattern showing cool and moist air is representative of a region of heavy rain that took place a day prior to these measurements (Data Image 4). Airborne measurements and surface observations taken by NCAR's Integrated Surface Flux Facility (ISFF) will be used to understand the implications of variations in surface soil moisture on the boundary layer and how well models can replicate this type of forcing. A goal of these boundary layer studies was to understand how surface heteorogeity leads to variations in atmospheric heat and moisture and eventually to storm formation. In addition to potentially improving weather prediction, such analysis also allows us to address the long standing question of whether boundaries between irrigated and non-irrigated crop lands are significant from a weather standpoint.

Nocturnal Convection

Data Image 5 shows radar reflectivity from a composite of operational and research radars over the region for a long-lived nocturnal convective system. The reader should note the reflectivity features that race southward out of the storm moving from Kansas and Colorado toward Texas. In contrast to the large-scale horizontal map shown in Data Image 5, Data Images 6 and 7 show horizontal and vertical cross-sections of reflectivity and velocity data from NCAR's S-Pol radar showing the wave structure of this event.

Signal to noise (i.e., a measure of reflectivity), vertical motion, and horizontal wind data from NCAR's MAPR profiler clearly show the wave motion in Data Image 8. However, a careful examination of these data shows the event to be associated with upward motions are stronger than the downward motions leading to a general upward displacement associated with this wave packet. Water vapor measurements taken by the French Leandre lidar pointed downward from the NRL P-3 in Data Image 9 also show this tendency as the water vapor field deepens dramatically as the aircraft moves toward the system (the convective system would lie off the right-hand-side of this figure). A working hypothesis is that this event represents a undular bore. During IHOP_2002, these events were quite common only during the nighttime hours. An important implication of these measurements is that the convection modifies its own inflow lifting the air to dramatically reduce the stability and deepen the depth of the moisture of air flowing toward into the storm. These changes are favorable for deep convection so that in principal a storm may modifiy its surroundings to make it more likely for the storm to continue. Thus the storms provide their own forcing mechanism to overcome the radiational stabilization of the airmass during the night.