Blog Layout

TONS OF INFORMATION

TONS OF INFORMATION

 

About fifty blogs are offered here for visitors to download and/or print.  Each individual blog, with links to references which (if not under a publisher's copyright) can also be downloaded and printed from this site, summarizes a specific aspect from a chosen set of topics.  A smaller number of “one-pagers” will address topics from my earlier fundamental book Integrated Aircraft Navigation.  An additional few will deal with topics not covered in either of those two books.  An example of the latter publicizes some useful facets of the ultra-familiar classical low-pass filter which (believe it or not – after all these years) have remained obscure.  The overall span of subjects (all firmly supported by experience as well as theory) ranges from elementary to advanced, in some cases relatively new and therefore largely unknown.


Modern estimation in both block (weighted least squares) and sequential (Kalman filtering, with Battin's derivation - much easier to follow than Kalman's) form, with their interrelationship developed quite far, enabling "plant noise" levels to be prescribed in closed-form, also providing highly unusual insight into sequentially correlated measurement errors; chi-squared residuals; implications of optimality during transients; need for conservatism in modeling; sensitivity of matrix-vs-vector extrapolation ("do's and don'ts"); application-dependence of commonality and uniqueness features; quantification

of observability and effects of augmentation on it; duality among a wide scope of navigation modes; commonly overlooked duality between tracking and short-term inertial nav error propagation; when "correction-to-the-adjustment"

terms can and can't be omitted; suboptimal (equal-eigenvalues) estimation with steady-state performance  indistinguishable from optimal; all fully supported by theory and experience


Basic building-blocks for attitude expressions: superiority of quaternions and direction cosines over Euler angles, due to singularity ("gimbal lock" at 90-deg for x-y-z sequence) and at 0-deg for z-x-z sequences used for orbits


GPS issues related to the top-priority goal of robustness: beyond elementary (4-state and 8-state) formulations; duality of pseudorange and phase ambiguity; exploitation of modern processing capabilities in GPS/GNSS receivers; carrier phase as integrated doppler vs frequency data; 1-sec sequential phase changes (MUCH easier to mix across constellations, negligible sequential changes in IONO/TROPO propagation, ambiguity resolution not needed, instant reacquisition, no-mask angle needed); streaming velocity for dead reckoning with segmentation of position fixes; differential operation -- differencing across satellites, receivers, and time; handling correlations from differencing; orthogonalization for simple QR factorization; measurement relocation in time and lever-arm adjustment; E(Extended)RAIM; D(Differential)RAIM; necessity of weighting in single-measurement RAIM with pseudoranges and carrier phases, concurrently; sample flight test results showing state-of-the-art accuracies in dynamics (e.g., cm/sec RMS velocity error and tenths-mrad leveling) with a low-cost IMU; revisit of the same flight segment, achieving decimeter/sec RMS velocity error without any IMU


Tracking (with subdivision into more than fifteen topics including a littoral environment operation with hundreds of ships present; orbit determination; usage of Lambert's law; surface-to-air (subdivided into ground-to-air and tracking from ships), surface-to-surface (again with the same subdivision), air-to-surface, air-to-air; reentry vehicles; usage of stable coordinate frames; linearity in both dynamics and measurements; Mode-S squitters for mutual surveillance and collision avoidance in crowded airspace; multiple track output usage (placement of gates, antenna steering, file maintenance); crucial importance of transmitting measurements rather than coordinates; extension to noncooperative objects, critical distinction (elsewhere blurred) between errors in tracking and stabilization; sucessfully accomplished concurrent track of

multiple objects with electronically steered beams; bistatic and multistatic operation; postprocessing to form familiar parameters from estimator outputs; short-range projectiles over "flat-earth" - plus many more)


Processing of inertial data - incrementing of position, velocity, attitude; straightforward state-of-the-art algorithms for complete metamorphosis from raw gyro and accelerometer samples into final 3-D position, velocity, and attitude; motion-sensitive inertial instrument errors; coning; sculling; critical distinction between misalignment (imperfect mechanical mounting) vs misorientation; adaptive accommodation of gyro scale factor and misalignment errors; instability of unaided vertical channel; azimuth pseudomeasurement; near-universal misconceptions connected to free-inertial coast


Support functions (transfer alignment; SAR motion compensation; stabilization of images; sensor control mechanizations; synchronization; determination of track retention probability)


Vision-for-the-future with maximum situation awareness for all cooperating participants in a scenario; Role of Interface (implications of singularities, RAIM, Differential GPS, etc.), software modularity, reuse, coordination).

By James Farrell 09 May, 2023
A look back in time by James L Farrell, PHD - 2023
11 Apr, 2020
Apologies for little posting lately. Much activity included some with deadlines; this will focus primarily on the few years leading up to Covid.
11 Apr, 2020
GNSS Aided Navigation & Tracking
By James Farrell 30 Aug, 2018
Apologies for little posting lately. Much activity included some with deadlines; this will be limited to the past twelve months. In 2017 my involvement in the annual GNSS+ Conference again included teaching the satnav/inertial integration tutorial sessions with OhioU Prof. Frank vanGraas. Part I and Part II are likewise being offered for Sept 2018. Also...Read More
28 Jun, 2018
Once again I am privileged to work with Ohio University Prof. Frank vanGraas, in presenting tutorial sessions at the Institute of Navigation’s GNSS-19 conference. In 2019, as in several consecutive previous years, two sessions will cover integrated navigation with Kalman filtering.  Descriptions of the part 1 session and part 2 session are now available online. By way of...Read More
30 Apr, 2018
The Institute of Navigation’s GNSS+ 2018 Conference provides me the privilege of collaborating with two of the industry’s pillars of expertise. Ohio University Professor Frank van Graas and I are offering fundamental and advanced tutorials.  Then on the last day of the conference I’m coauthored with William Woodward, Chairman of SAE Int’l Aerospace Avionics Systems Division and hardware lead...Read More
24 Apr, 2018
A new SAE standard for GPS receivers is a natural complement to a newly receptive posture toward innovation unmistakably expressed at high levels in FAA and Mitre (ICNS 2018).  Techniques introduced over decades by this author (many on this site) can finally become operational. 1980s euphoria over GPS success was understandable but decision-makers, lulled into complacency, defined requirements in adherence...Read More
22 Mar, 2018
At April’s ICNS meeting (Integrated Communications Navigation and Surveillance) as coauthor with Bill Woodward (Chairman, SAE International Aerospace Avionics Systems Division), I’ll present “NEW INTERFACE REQUIREMENTS: IMPLICATIONS for FUTURE“.  By “future” we indicate the initiation of a task to conclude with a SAE standard that will necessitate appearance of separate satellite measurements to be included...Read More
16 Jul, 2016
A recent video describes a pair of long-awaited developments that promise dramatic benefits in achievable navigation and tracking performance.  Marked improvements will occur, not only in accuracy and availability; over four decades this topic has arisen in connection with myriad operations, many documented in material cited from other blogs here. 
12 Feb, 2016
For reasons, consider a line from a song in Gilbert-&-Sullivan’s Gondoliers: “When everybody is somebody, then nobody is anybody” — (too many cooks) For consequences, consider this question: Should an intolerable reality remain indefinitely intolerable? While much of the advocacy expressed in my publications and website have focused on tracking and navigation, this tract concentrates...Read More
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