INERTIAL INSTRUMENT SYSTEM FOR AERIAL SURVEYING U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1390 Inertial Instrument System for Aerial Surveying By RUSSELL H. BROWN, with contributions by WILLIAM H. CHAPMAN, WILLIAM F. HANNA, CHARLES E. MONGAN, U.S. Geological Survey, and JOHN W. HURSH, The Charles Stark Draper Laboratory, Inc. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1390 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1987 DEPARTMENT OF THE INTERIOR DONALD PAUL HODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging-in-Publication Data Brown, Russell H. Inertial instrument system for aerial surveying. (U.S. Geological Survey professional paper ; 1390) Bibliography : p. 95 Includes index. Supt. of Docs, no.: I 19.16:1390 1. Aerial photogrammetry Equipment and supplies. 2. Inertial navigation systems I. Title. II. Series. TA593.35.B76 1987 526.9'823 85-600134 For sale by the Books and Open-File Reports Section, U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 FOREWORD In the late 1960's and early 1970's, the much-heralded and precise perfor mance of inertial guidance systems in space exploration challenged earth sci entists to seek ways of turning those systems to their advantage in the near- earth environment. Russell Brown and Charles Mongan sensed and responded to that challenge. Over a 2-year period (1972-74), they shaped a workable research task and secured the endorsement of the top U.S. Geological Survey managers. As a result, the Geological Survey was committed to the develop ment of a pioneering inertial instrument system for aerial surveying, through contract arrangements with The Charles Stark Draper Laboratory. The formal contract work began in mid-1974, at a time when a few military and civilian agencies were successfully operating less-precise generations of inertial guidance systems in motor vehicles and helicopters to establish control lines for topographic surveys. The Geological Survey's research commitment was to move rapidly beyond those techniques and to field a new and more precise inertial guidance system capable of obtaining similar or better control lines from a fixed-wing aircraft. The potential savings in dollars, manpower, and time in using the new system for field studies in the Geological Survey Operating Divisions more than justified this research commitment. After nearly a decade of work, a prototype model of this new instrument system has been successfully flight tested. Its demonstrated performance has exceeded in every respect the stringent design specifications. Although the full range in performance capabilities remains to be explored, the system will provide highly efficient, cost-effective support for scientific programs of the Geological Survey, including production of topographic maps, investigations of water resources, and assessment of mineral resources and geologic hazards. The system also has immediate potential to support the research and opera tional missions of other Federal, State, local, and private organizations. The Geological Survey is pleased to have played a major developmental role in this important scientific achievement. Dallas L. Peck Director PREFACE The purpose of this report is to describe, for the nonspecialist earth scientist or engineer, an inertial guidance or navigation system that will enable use of relatively light aircraft for efficient nationwide data-gathering in geology, hydrology, terrain mapping, and gravity-field mapping. Development of this airborne instrument system is a logical consequence of the phenomenal post- World-War-II growth in the science and technology of inertial guidance sys tems. That growth, although obviously predestined by the genius of men like Dr. Charles Stark Draper, was accelerated by the onset of the international space race in the 1960's. By the early 1970's, new generations of gyroscopes and accelerometers key components in inertial systems had been designed, built, laboratory proven, and field tested sufficiently to allow application of inertial systems to certain high-precision field measurement processes in the earth sciences. Prime exam ples of successful applications in that period include the military development of a position and azimuth determining system, to run survey control lines, and the development for the National Aeronautics and Space Adminstration of the inertial navigators that guided the round-trip Apollo flights to the Moon. In these applications, however, the precision levels were lower than what the U.S. Geological Survey would require for its use. The first inertially guided transcontinental flight, from Boston to Los Ange les, occurred in February 1953 with an Air Force B-29 carrying an inertial navigator that weighed more than a ton (over 900 kilograms). Dr. Draper (system designer), John Hursh (system operator), Charles Collins (pilot), and Irving Levin (flight engineer) were among The Charles Stark Draper Labora tory contingent that comprised that historic crew, and all have been involved actively in the current Geological Survey project. The present-generation iner tial navigators in regular airline use individually weigh less than 100 pounds (45 kilograms) and can be accommodated in a space roughly equivalent to a desk file drawer. In a timespan of about two decades, this kind of evolution in inertial system design, with equally graphic improvements in precision, has made the current instrument-development project technically feasible. Not only did feasibility crystallize, but the bright prospects that relate to the continuing evolutionary trend in inertial navigator design virtually guarantee that an instrument system built to satisfy the present Geological Survey specifications for preci sion can be upgraded periodically to meet even more stringent specifications whenever cost-effectiveness criteria dictate. The instrument system described in this volume capitalizes not only on virtual state-of-the-art inertial guidance technology but also on similarly ad vanced technology for measuring distance with electromagnetic radiating devices. The distance measurement can be made with a transceiver beamed at either a cooperative target, with a specially designed reflecting surface, or a noncooperative target, such as the Earth's surface. The instrument system described herein features components that use both techniques. Thus, a laser tracker device, which updates the inertial guidance unit or navigator in flight, makes distance measurements to a retroreflector target mounted at a ground- control point; a laser profiler device, beamed vertically downward, makes dis tance measurements to the Earth's surface along a path that roughly mirrors the aircraft flight path. In both technological domains, inertial guidance and electromagnetic distance measuring, the equipment components selected for use in this new instrument system were advanced well beyond levels that were then commercially available. CONTENTS (cid:9)Page Page Foreword ------------------------------------------------ in Computer Continued Preface -------------------------------------------------- v Peripheral devices ------------------- 53 Commonly used inch-pound terms and their Software ---------------------------- 54 preferred SI equivalents -------------------------------- ix Laser profiler ----------------------------- 66 List of abbreviations -------------------------------------- ix Color television camera -------------------- 73 Abstract ------------------------------------------------- l Special role of gravity ------------------------- 74 Introduction --------------------------------------------- 2 Aircraft for deployment of the instrument system 76 Developmental incentives ----------------------------- 2 Operation of the instrument system ------------ 77 Developmental strategy ------------------------------- 2 Ground control ---------------------------- 79 Developmental history -------------------------------- 3 Flight planning --------------------------- 81 Acknowledgments ---------------------------------------- 6 Flight mission ---------------------------- 83 Instrument system --------------------------------------- 7 Maintenance and service ------------------- 84 Overall system concept ------------------------------- 7 Postflight data processing ---------------------- 84 Inertial navigator ------------------------------------ 8 Performance-evaluation flights ----------------- 85 Inertial measurement unit -------------------------- 9 Overall objectives ------------------------- 85 Gyroscopes ------------------------------------- 10 Calibration range ------------------------- 85 Accelerometers --------------------------------- 15 Specified flights --------------------------- 87 Gimbal system --------------------------------- 19 Flight results ----------------------------- 89 Resolvers -------------------------------------- 19 Flights 1 and 2 ------------------------ 89 Feedback loops --------------------------------- 23 Flights 3 and 4------------------------ 89 Electronics ------------------------------------- 24 Uses for the instrument system ---------------- 91 Temperature control ---------------------------- 25 Hydrologic studies ------------------------- 91 Performance dynamics ------------------------------ 27 Map production tasks ---------------------- 92 External measurement requirement ----------------- 35 Geologic studies --------------------------- 93 Laser tracker -------------------------------------- 36 Future improvements in the instrument system - 93 Computer ------------------------------------------ 46 Selected references ---------------------------- 95 Physical attributes ----------------------------- 47 Symbols and dimensions ----------------------- 96 Subsystems and data interfaces ----------------- 50 Index ----------------------------------------- 98 ILLUSTRATIONS Page FIGURE 1. Fiscal year history of work on U.S. Geological Survey contract by Draper Laboratory, Cambridge, Mass., 1975-81 -- 5 2. Frequency response characteristics of inertial navigator and tracker to vehicle motion --------------------------- 8 3. Schematic of gyro and gimbal-support structure --------------------------------------------------------------- 10 4. Schematic of single-degree-of-freedom gyro -------------------------------------------------------------------- 11 5. Photograph showing the single-degree-of-freedom floated gyro -------------------------------------------------- 13 6. Schematic of gyro and accelerometer arrays for aerial profiling of terrain system -------------------------------- 15 7. Schematics of acceleration-measuring devices ------------------------------------------------------------------ 16 8. Schematic view of the single-axis pendulous integrating gyro accelerometer ------------------------------------- 17 9. Photograph showing the pendulous integrating gyro accelerometer ---------------------------------------------- 18 10. Schematic of support structure for inertial measurement unit --------------------------------------------------- 20 11. Resolver schematic and nomenclature ------------------------------------------------------------------------- 21 12. Photograph showing disassembled multispeed resolver for gimbal-support structure ------------------------------ 22 13. Schematized feedback loops ---------------------------------------------------------------------------------- 23 14. Schematic diagram of electrical circuits for stabilization subsystem of inertial measurement unit ----------------- 25 15. Thermal control schematic for inertial measurement unit ------------------------------------------------------ 26 16. Support and thermal control structure for inertial measurement unit ------------------------------------------- 28 17. Orientation of locally level three-coordinate reference scheme at selected points on an idealized ellipsoidal Earth -- 30 18. Schematic of support structure for inertial measurement unit and tracker --------------------------------------- 37 19. Photograph showing the inertial measurement unit, laser tracker, gimbal-support structure, and housing --------- 39 20. Optical layout for laser tracker ------------------------------------------------------------------------------- 40 21. Analysis of the range equation for the laser tracker ------------------------------------------------------------ 42 22. Principal reference frequencies used in the aerial profiling of terrain system ------------------------------------- 44 23. Cone-shaped air space within which the tracker can see a retroreflector target ----------------------------------- 45 24. Photograph showing principal components and final assembly of the U.S. Geological Survey-designed retroreflector 46 25. Functional structure of the aerial profiling of terrain system computer with connections to subsystems and (cid:9)peripheral devices --------------------------------------------------------------------------------------- 47 26. Photograph showing the packaged flight computer for the aerial profiling of terrain system ----------------------- 49 27. Photograph showing the operator's keyboard and plasma display terminal for the aerial profiling of terrain system 52 28. Photograph showing the line printer for the aerial profiling of terrain system ------------------------------------ 53 29. Photograph showing the magnetic tape controller for the aerial profiling of terrain system ----------------------- 54 30. Photograph showing the magnetic tape recorder for the aerial profiling of terrain system ------------------------- 55 31. Hypothetical sequence of the aerial profiling of terrain system modes for a flight mission ------------------------- 56 32. Structure graph of the master operating program for the aerial profiling of terrain system ------------------------ 61 INSTRUMENT SYSTEM FOR AERIAL SURVEYING 33. Recurrence intervals and callup sequence for the five synchronous tasks in the aerial profiling of terrain system ---- 66 34. Data flow for the STARTUP AND TEST mode of the software for the aerial profiling of terrain system ------------- 67 35. Data flow for the CALIBRATE AND ALINE and STANDBY modes of the software for the aerial profiling of (cid:9)terrain system -------------------------------------------------------------------------------------------- 68 36. Data flow for the four flight modes of the software for the aerial profiling of terrain system ------------------------ 69 37. Photograph showing basic chassis with optics and some electronics for the laser profiler --------------------------- 71 38. Analysis of the range equation for the laser profiler ------------------------------------------------------------- 72 39. Photograph showing color television camera for the aerial profiling of terrain system ----------------------------- 74 40. Photograph showing video recorder and control box for the aerial profiling of terrain system ----------------------- 75 41. Photograph showing time-date and time-code generators for the aerial profiling of terrain system ------------------ 76 42. Photograph showing DeHavilland Twin Otter aircraft ----------------------------------------------------------- 79 43. Arrangement of aerial profiling of terrain system components in DeHavilland Twin Otter aircraft ----------------- 80 44. Flight-path layout for profiling the Farmington River flood plain near Avon, Conn ------------------------------- 82 45. Information flow through postmission data-processing software -------------------------------------------------- 84 46. Control diagram and retroreflector sites for calibration range ---------------------------------------------------- 86 47. Flight plan for performance-evaluation flights 1 and 2 ---------------------------------------------------------- 88 48. Flight plan for performance-evaluation flight 3 ----------------------------------------------------------------- 88 49. Flight plan for performance-evaluation flight 4 ----------------------------------------------------------------- 88 TABLES (cid:9)Page TABLE 1. Package size and power requirements for the aerial profiling of terrain system computer and peripherals __..---------- 48 2. Computer-action summary for the 14 special tasks in the aerial profiling of terrain system -------------------------- 62 3. Factors bearing upon aircraft selection ---------------------------------------------------------------------------- 77 4. Performance characteristics, DeHavilland Twin Otter aircraft ------------------------------------------------------- 78 5. Position coordinates and gravity values for retroreflector sites in the calibration range -------------------------------- 87 6. Results of performance-evaluation flights 1 and 2 ------------------------------------------------------------------ 90 7. Results of performance-evaluation flights 3 and 4 ------------------------------------------------------------------ 91 Commonly used Inch-Pound terms and their List Of Abbreviations preferred SI equivalents Multiply inch-pound units By To obtain SI equivalent Abbreviation Explanation Length inch (in.) 2.540 x 10*a millimeter (mm) APT(S) aerial profiling of terrain (system) foot (ft) 3.048 x 10-! meter (m)** yard (yd) 9.144 x 10-1 meter (m) mile (mi) 1.609 kilometer (km) DC direct current nautical mile (nmi) 1.852* kilometer (km) Area DMA direct memory access square foot (ft2) 9.290 x 10-2 square meter (m2) GaAs gallium arsenide Volume cubic foot (ft3) 2.832 x 10-2 cubic meter (m3) gyro gyroscope Mass Hz hertz ounce, avoirdupois (oz) 2.835 x 10 gram (g) pound, avoirdupois (Ib) 4.536 x 10-! kilogram (kg)** IMU inertial measurement unit Force I/O input/output ounce-force (ozf) 2.780 x lO-1 newton (N) pound force (Ibf) 4.448 newton (N) kHz kilohertz Pressure pound per square inch (lb/in.2) 6.895 x 103 pascal (Pa) MHz megahertz pound per square foot (lb/ft2) 4.788 x 10 pascal (Pa) bar 1 x 105* pascal (Pa) millimeter of mercury (0°C) 1.333 x 102 pascal (Pa) ms millisecond inch of mercury (0°C) 3.386 x 103 pascal (Pa) Torque |XS microsecond ounce-inch (oz-in.) 7.062 x lO-3 newton meter (N-m) ns nanosecond pound-foot (lb-ft) 1.356 newton meter (N-m) dyne centimeter (dyn-cm) 1 x 10-7* newton meter (N-m) NAD North American Datum Temperature degree Fahrenheit (°F) Temp °C = (Temp °F - 32)(5/9) degree Celsius (°C) NGVD National Geodetic Vertical Datum Illumination rpm revolutions per minute foot-candle (ft-c) 1.076 x 10 lux (Ix) *Exact conversion factor. TV television **Basic SI unit. aExact conversion, except for geodetic surveying in the United States for which the conver sion factor is 2.540005. V volt W watt