Home Articles Design, Development and Operation of an Airborne Multispectral Sensor as a Multidisciplinary...

Design, Development and Operation of an Airborne Multispectral Sensor as a Multidisciplinary Educational Project

Bjorn F. Dahlen
E-Mail: [email protected]

Doug Olsen
Email: [email protected]

John D. Odegard School of Aerospace Sciences
University of North Dakota
Grand Forks, ND 58202

Abstract
The Airborne Environmental Research Observational Camera (AEROCam) is an airborne sensor flown on light aircraft to collect Multispectral imagery in four spectral with a one-meter ground sampling distance. The AEROCam research and development effort was initiated by the Upper Midwest Aerospace Consortium (UMAC), which analyzes satellite imagery for regional farmers, ranchers, and natural resource managers. This sensor represents the first of several data acquisition technologies under development for gathering specific information for UMAC's end users. Design, ongoing development and operations of the AEROCam system are being conducted by a multidisciplinary team of students and faculty at the University of North Dakota (UND) and John D. Odegard School of Aerospace Sciences. The technical management team consists of faculty and graduate students providing guidance to the undergraduate students. The research, design, development and daily operation of AEROCam provides valuable experiential learning opportunities for students and a unique blend of real world applications in an academic environment.

Introduction
The Airborne Environmental Research Observational Camera (AEROCam) is a four-band high resolution multispectral sensor designed specifically for flight on University of North Dakota airplanes. The sensor is used to gather remote sensing imagery for precision agriculture and environmental science missions. Two colleges at UND, the John D. Odegard School of Aerospace Sciences and the School of Engineering & Mines, have collaborated on the design and development of the AEROCam sensor. Students and faculty within UND Engineering are responsible for designing, building, and testing the instrument, while funding and program operations and management are provided by UND Aerospace through the NASA-supported Center for People and the Environment (CP&E). This research center is operated by the Upper Midwest Aerospace Consortium (UMAC), based at the University of North Dakota.

UND Aerospace maintains and operates a fleet of over 100 small aircraft in the leading four-year aviation program in the country. Through a versatile design concept, UND fleet aircraft – specifically one the modern Piper Arrow airplanes – can be available within a matter of hours to gather multispectral imagery for farmers and researchers throughout the Upper Midwest. Rapid response to request is a key objective. Data acquisition flights will be flown by an on-call UND pilot. The imagery will be then be post-processed and delivered to end users via the Internet.

The Upper Midwest Aerospace Consortium serves a large number of farmers, ranchers, and foresters throughout the region, and UMAC researchers are currently interested in developing customized remote sensing technologies that are truly driven by their end users' needs. The Upper Midwest is known world-wide for its excellent farming and ranching production, and precision agriculture techniques such as variable rate fertilizer application and strategic grazing can provide even higher yields at a significant cost savings, while simultaneously minimizing environmental impact. Unfortunately, the Upper Midwest is also known for its extremes in weather, including severe blizzards, drought, and windstorms, resulting in disasters such as flooding, forest fires, and deforestation. Active remote sensing satellites do not currently satisfy the high-resolution, high-frequency revisit, and fast data delivery requirements of precision agriculture and disaster response end users within the Upper Midwest. The sensor has been designed to meet the specific data needs of UMAC's end users.

From an educational perspective, this experiential learning project has exposed the students to many concepts that simply cannot be introduced in conventional lecture and laboratory courses. From proper documentation techniques and the systems engineering philosophy to teamwork and systems-level integration, students (and faculty) learned valuable lessons in both the technical aspects of design, development and operating an airborne sensor. The multidisciplinary teaming of electrical and mechanical engineering students and faculty, remote sensing researchers, and aviation support personnel has provided all of the team members with an excellent "real-world" product development experience from within an academic setting.

System Overview:
Airborne Environmental Research Observational Camera, or AEROCam, is a multispectral airborne digital imaging system, capable of acquiring data in four visible and near-infrared bands. The imaging core of the system is a set of four Dalsa CA-D4 area scan digital cameras that feature a 1024 x 1024 CCD array of 12-micron pixels, with 8-bit quantization. The center frequencies (and bandwidths) of the filters selected for initial operations are 500nm (70nm), 550 nm (70nm), 660 (40nm), and 850 (40nm). An alternative filter at 720 (12.6nm) is also available. At nominal altitudes and 17 mm lenses, images have a ground spatial resolution of 1 meter, with a field of view of about 1/2 square mile. Altitude, lenses, and filters can be changed to accommodate special needs.

Electrical and Mechanical Subsystems
The AEROCam sensor is fully self-contained; other than physical mounting, there are no connections power, data, or otherwise to the on-board aircraft systems. The entire system consists of an avionics rack, which replaces the rear seats in the airplane; the camera pod, situated outside the luggage door; a DGPS antenna mast extending above the camera pod; and a flat-panel screen for use by the pilot and/or operator inside the cockpit.

Four area-scan digital imaging cameras are mounted in the external pod. Each camera has a unique bandpass filter within the lens mounting adapter. An inertial measurement unit, the INS sensor that measures roll, pitch, and yaw, is also installed in the pod with the cameras. A single differential GPS antenna is mounted at the top of a mast extending from the pod. Power and data cables run along the pod arm to the equipment racks.

Multidisciplinary learning opportunities
The AEROCam project taught the students important lessons in teamwork and its necessity in the successful completion of large-scale projects. Team members had significantly more responsibility and accountability placed on their shoulders than they had ever encountered previously student project. They were responsible for making decisions on everything from the user requirements and the components used in each subsystem to the FAA certification process and how to begin mission operations. Students learned how to make informed group decisions and to deal with the ramifications of these decisions. Since each student was responsible for a major portion of a subsystem, he or she also learned how to depend on others to complete the mission. If only one person did not fulfill his/her tasks, the mission would be unsuccessful. Part of the interdependence of the team members was grounded in the system integration and test deadlines. Delaying one test of a subsystem directly impacted everyone else's schedules.

Beyond the system design and construction, students learned how to polish the "soft skills," which are vitally important in today's business world. Soft skills, including oral, written, and interpersonal communications, can be the most important skills that a person develops in order to advance their career. Working in large groups as a part of the undergraduate and graduate curricula provides students with a chance to hone their people skill. From weekly face-to-face progress meetings, to teleconferences with the NASA researchers and FAA engineering representatives, and media reports, the students learned from experience how they must work together as a team to accomplish their goal of getting customized remote sensing data into the hands of precision farmers, ranchers, and foresters.

Project Summary and future plans
The AEROCam sensor has provided a number of opportunities for students at the University of North Dakota to conduct real-world R&D within an academic environment. In the process of enhancing their technical skills, they were also forced to practice their oral, written, and interpersonal communication skills. Moreover, the students, faculty, and staff learned how to work together as a team to accomplish a common goal. To design, build and test a instrument of this complexity at such a low cost compared to a commercial venture, the contribution of every team member becomes critically important.

A plethora of research and development tasks related to AEROCam await the students over the next several years:

  • Geometric and radiometric camera calibration;
  • Software modifications for ground-based automated image geo-correction;
  • Conversion of the raw data into a useful map product in the GeoTIFF image format, which can be imported into most geographic information system (GIS) software packages;
  • Implementation and test of the DGPS/INS Kalman estimation algorithm, to improve the accuracy of position and attitude measurements;
  • Examination of the possibility of interfacing to the aircraft power system for longer flights, rather than using an independent (and very heavy) battery to power the sensor;
  • Investigation of using a carrier-phase DGPS for highly-accurate position measurements;
  • Image analysis of the remote sensing data and precision agriculture data distribution via the Internet;
  • Addition of a long-wave infrared (LWIR) camera for thermal imaging applications and a hyperspectral sensor.

The UND Aerospace/Engineering partnership is a model for future growth in remote sensing research and development in an educational setting. Plans are in the works to design, build, test, and operate new airborne and spaceborne remote sensing instruments. The success of AEROCam has led to a new project: Agricultural Camera (AgCam), a two-band sensor that will be operated as a payload on the International Space Station's Window Observational Research Facility (WORF).