NSF COLDEX Level1B GPS/IMU derived post processed aircraft trajectories

<article>
<header>
<h2>NSF COLDEX GPS/IMU Level 1B Airborne Position and Attitude Solutions</h2>
</header>

<p>
These data are results processed using Hexagon | NovAtel's Waypoint Inertial Explorer, a GUI
environment for performing joint Inertial Measurement Unit (IMU) / Global Positioning System (GPS)
kinematic position and attitude solutions. The raw data used for creating these solutions is at <a href="https://doi.org/10.15784/601933" target="_blank" rel="noopener noreferrer"> Young et al., 2025 [USAP-DC] </a>. Manual steps included cutting out bad portions of data and removing bad GPS satellite range information. Only the US GPS constellation of satellites was used.
</p>

<p>Two types of solution are provided.</p>

<section>
<em>wpt1</em> solutions are produced by jointly processed IMU rotation rate and acceleration data with GPS
data using a Kalman filter to produce an internally consistent position and aircraft attitude solution at the
center of the IMU unit at a rate of 50 Hz. Loosely coupled solutions first perform kinematic precise point
positioning (PPP) solving the GPS range data for 1 Hz positions, and then fit the IMU data to interpolate
positions and find attitude. Tightly coupled solutions incorporate the IMU data into the position solutions.
Accuracies are typically on the order of a few cm.
</p>
</section>

<section>
<em>wpt2</em> solutions only have the PPP position solution, and provide redundancy in the case of an IMU issue.
These produce data at the rate of the GNSS receiver (typically 1–2 Hz).
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</section>

<section>
<p>Files have the following name convention:</p>
<code>SEASON_PLATFORM_FLIGHT_PROCESSING.wpt#</code>
<p>
Here the <code>SEASON</code> is either <em>CXA1</em> (the 2022–23 NSF COLDEX airborne season) or
<em>CXA2</em> (the 2023–24 NSF COLDEX airborne season); the <code>PLATFORM</code> is the GNSS
antenna/receiver combination; the <code>FLIGHT</code> is the flight number within the season; and the
<em>PROCESSING</em> is either <em>LCPPP</em> (loosely coupled with PPP), <em>TCPPP</em> (tightly
coupled with PPP), or <em>PPP</em> (PPP only). Some flights have multiple files due to system restarts;
other files span multiple flights due to short turn around between flights.
</p>
</section>

<section>
A file called POS_timelimits.csv contains the start and end time of each file in seconds with respect to the UNIX epoch.
</section>

<section>
The files are in the form of tables with headers and footers delimited with the <code>#</code> character.
Column names are internally defined.
</p>
</section>
</article>