CReSIS
The Center for Remote Sensing of Ice Sheets (CReSIS) is a Science and Technology Center established by the NSF in 2005, with the mission of developing new technologies and computer models to measure and predict the response of sea level change to the mass balance of ice sheets in Polar Regions.
Overview
CReSIS comprises six academic partner institutions, with the headquarters located at the University of Kansas, which is the lead institution. The other academic partner institutions are Elizabeth City State University, The Pennsylvania State University, Indiana University, Los Alamos National Laboratory, University of Washington, and the Association of Computer and Information Science Engineering Departments at Minority Institutions. In addition to this core group, CReSIS collaborates with several international institutions and industry partners. For scientists worldwide, CReSIS is a primary source of data on polar ice sheet thickness and other properties. The development of Sensors and Platforms for Manned and Unmanned Cryospheric Remote Sensing enhance KU’s role at the forefront of the global climate change research.
Manned Platforms
In support of the NASA ICEbridge campaign, University of Kansas and DARCorporation researchers equipped the NASA Dryden DC8 and the NASA Wallops P3 with extensive radar arrays comprising accumulation, snow, KU-band, and the multi-channel coherent radar depth sounder (Mcords) antennas. Again, the use of composite structures is required to tailor the distribution of relative permittivity for radar performance, as well as to ensure structural, aerodynamic and aircraft performance requirements are met.
For the NASA DC-8, the two main fairing design drivers were preventing shockwave formation and minimizing aerodynamic drag loads. Due to the transonic flight regime of the DC-8 much care was given to the external shape of the fairing to prevent shocks from forming, and the resulting shapes lend themselves to composite manufacturing. Structural elements above the radiating antennas are electrically conductive, while those below and parallel to the radiating antennas have low relative permittivity. To the best of our knowledge this is the first radar sounder/imager flown successfully over the polar ice sheets on a turbojet aircraft and from high altitude.
For the NASA P-3B, analyses were completed not only to determine the range reduction of the aircraft and the aerodynamic loads used for structural sizing of the fairing, but also to determine the effects of the presence of the fairing on the stability and control of the aircraft. The size of the wing-mounted fairing was limited due to the need for adequate separation between the fairings, the propellers, and the wing tips. The turbulent flow behind the propeller (prop wash) and from wing tip vortices can increase the drag of the fairing and potentially fatigue the structure due to the series of impinging pressure waves. In this case the lower surface of the wing is used as the reflective ground plane, and so structural elements above, below and parallel to the radiating antennas have low relative permittivity. Thicknesses of composite structures are tailored to the local frequencies of the radiating antenna elements. To the best of our knowledge this is the largest ice radar sounder/imager array flown successfully over the polar ice sheets.
Each of these installations involved high-fidelity, physics-based, interdisciplinary simulations for geometry, aerodynamic loads, aircraft performance, static and dynamic structural response, and radar performance. In each case the design and fabrication of the antennas and the aircraft integration structures were undertaken by the researchers at the University of Kansas with significant involvement of graduate and undergraduate students in Aerospace and Electrical Engineering. To date, these aircraft and these instruments have flown more than 48 science flights, totaling more than 440 hours in Greenland and Antarctica, massing in excess of 150,000 flight nm and enabling collection of over 235TB of unique data for ice bed topography and internal layering. We continue to develop new sensors and platforms, and to operate these platforms to develop unique data sets for the broad scientific community.
Unmanned Platforms
Researchers at the NSF-supported Center for Remote Sensing of Ice Sheets (CReSIS) have developed a new unmanned aircraft system (UAS) called Meridian that is designed to enable extensive remote sensing surveys over isolated areas of Greenland and Antarctica. The base design requirements called for a portable aircraft capable of carrying a variety of payloads for missions from remote base camps in Antarctica and Greenland. This translated into requirements for a rugged, modular aircraft with removable wings that can be assembled in minimum time in the field. Aircraft rigidity constraints for the wing-mounted sensors and takeoff weight versus range performance lead to an aircraft of predominantly bonded carbon/epoxy composites. With a primary scientific payload of an ice-penetrating radar, the Meridian UAS will enable fine-scale mapping of ice thickness, internal layers, bed topography, and basal conditions. Meridian is particularly well-suited for survey areas that require long transit flights, close survey line spacing, and operation at low altitudes. The Meridian weighs 1,100 lbs, has a 26-foot wingspan, and a range of 950nm at the full 120 lbs payload capacity. Although the vehicle has been designed to optimize ice penetrating radar performance, additional payloads and sensors have also driven design to ensure ready adaptation to multi-mission science driven payloads.
We have also developed and operate the G1X UAS which is an 85lb, 17-foot wingspan vehicle with a range of approximately 60 nm per gallon of fuel. The aircraft can be configured with either wheels or skis; recent field trials in Antarctica were all on skis. The primary payload for this aircraft has been a dual frequency HF/VHF radar depth sounder, to enable sounding of ice in fast flowing glaciers.
University of Kansas faculty collaborators have effectively embedded immersive research experiences for all undergraduate students in aerospace engineering, with at least seventeen courses using Meridian and G1X UAS development as the basis for design projects, homework and examination content. Composite design, analysis and fabrication efforts address interdisciplinary design requirements for radar, aerodynamic, aircraft and structural performance, often requiring trades between physical and mechanical properties inherent in different classes of fiber reinforced materials. The wing mounted Vivaldi ice penetrating radar antennas, for instance, are layers of glass/epoxy, copper and carbon/epoxy designed to transmit and receive broadband VHF signals while maintaining displacement and modal excitation limits.