Everyone loves progress, but nobody likes change. However, change can be good, and for the society of land surveyors, 2022 brings some well-needed changes.
In 2022, the U.S. National Geodetic Survey (NGS) is set to modernize the National Spatial Reference System (NSRS) to a new datum known as North American Terrestrial Reference Frame (NATRF2022). The plan is to altogether remove our current three horizontal reference frames, NAD 83 (2011), NAD 83 (PA11), and NAD 83 (MA11), along with our vertical datum, North American Vertical Datum of 1988 (NAVD88). These datums need to be replaced due to a large number of deficiencies and shortcomings discovered over time.
First, let me explain why datums are essential. A datum is used to reduce errors when marking out and measuring the Earth’s surface. They initially begin with a fixed reference point or set of points, from which precise measurements can be collected. For land surveyors, these reference points are known as survey markers or benchmarks. These points are collected and combined into a network that forms the fundamental dataset for a survey reference frame. They are the basis for all geodetic surveying, mapping, and navigation.
A major problem with our current horizontal datum is that the primary benchmark was proven to be misaligned. The horizontal and geometric datum NAD83, originally published in 1986, was the very first national datum anywhere in the world to have its origin of coordinates at the Earth’s mass center, or geocentric. This was done by calculating a model of the Earth shaped like a perfect ellipsoid. Given the technology at the time, late 70’s early 80’s, our knowledge of the location of Earth’s-mass center was approximately a value of about 2.2 meters or around 7 feet. Not bad, but based on our newest positioning technology and scientific knowledge, we have discovered that Earth is not a perfect ellipsoid. This discovery has improved the accuracy from 2.2 meters down to about 2 or 3 centimeters.
A major problem with our current vertical datum is that it relies heavily on the original survey markers in the ground. Unfortunately, due to subsidence, uplift, freeze/thaw, many have invalid elevations from when they were originally set. The work it will take to relevel, remeasure, or even locate these benchmarks will be costly and time-consuming. NATRF2022 will help lessen the impact of these aging physical markers that currently help define NAVD88. The new datum will rely entirely on reference stations that continuously receive GPS information. Given your location, this will correct errors across the country from 0.5 to 1.5 meters.
These are just two of the significant deficiencies NATRF2022 is set to improve upon. Below is some additional advancement with the new datum:
- Obtain precise ellipsoid heights on NAVD88 benchmarks.
- Reduce all definitional & access-related errors in the geometric reference frame to 1 cm when using 15 min of GNSS data
- Orthometric heights accessed via GNSS accurate to 2 cm
- Combine ellipsoid height and geoid heights at the same point to calculate its elevation.
- Ability to compare time-dependent coordinates in any of the terrestrial reference frames at any epoch.
We need to make this change to address future mapping needs and positional accuracies efficiently. Here at Howell Kline Surveying, we hang our hat on planning for the future ahead. When it comes to these changes, we will be on the front line.