What kind of airspeed does a (3D) GPS measure?

Question

Assuming a GPS receiver is advanced enough to compute 3D position/velocity with reasonable accuracy, it can indicate not only the aircraft's ground speed (which ignores altitude changes), but something akin to airspeed as well. If there was no wind, this would be equivalent to true airspeed. In reality there would be wind so it is "TAS minus wind". Since this completely ignores the actual air (the value would have been the same if there were no atmosphere), however, calling it anything related to "airspeed" seems like a misnomer to me.

Is there a standard terminology for this kind of velocity measurement?

EDIT: It seems my question was quite vague and providing more detail about what I'm trying to do would help. I'm writing the documentation for a GPS-based tracking device, which would be used in fixed-wing aircraft. The GPS is exceptionally good, with very high precision and quick sampling rate. It even provides very accurate speed, which is Doppler-shift based AFAIK. This data will be sent through telemetry. I'm trying to label the data channels in a way that would be useful for aviators down on the surface, so I'm trying to familiarize myself with the proper terminology. Therefore if I label this ("3D") velocity as "airspeed" (indicated/true airspeed), it will be misleading. If I label it "ground speed" (which is 2D), it will be misleading as well. My question is only whether a standardized name for this type of velocity exists; if there's nothing widely used, I'll just coin a name of my own (e.g. "3D velocity") and explain it well enough in a tooltip.

Answer 1

Q: "What kind of airspeed does a GPS measure?"

A: "None whatsoever."

Answer 2

The GPS does not sense or compute any type of airspeed, (True, indicated, calibrated, etc.) it only knows the airplane's velocity relative to the earth's surface. (Actually, relative to geosynchronous satellites...) GPS units currently in use can do this in 3 dimensions.

There is both a horizontal and a vertical component to movement in 3D space. For general navigation purposes the pilot is only concerned with the horizontal, i.e. ground speed. (How fast am I going, and when will I get there?)

On some systems you can display vertical velocity from the GPS, but it is instantaneous and very jumpy, so it isn’t particularly helpful. The pressure driven VSI gauge is much more useful.

While it would be possible for a 3D system to compute velocity along a diagonal line between vertical and horizontal, this information is of no use to the pilot. The vertical component comes into play mainly in the approach phase, to compute and display glide slope information during RNAV approaches.

In the approach phase the GPS system uses a blend of horizontal and vertical navigation information to allow us to fly the “hypotenuse”, but we don’t think of it in terms of a velocity vector, much less an “airspeed”. It is more an imaginary line in space we are trying to track along in 3D with the system providing cues to help us know where we are relative to the published course and glideslope.

ADDENDUM PER QUESTION EDIT: Wind will have a far greater effect on this velocity vector than the minor climb and descent angles encountered during "normal" (non-aerobatic) flight. Without knowing your customer or exact purpose of the device you reference, I can say confidently that no aviation person would care about earth referenced velocity other than vectors in the horizontal or vertical. If the diagonal, (not airspeed) velocity was desired for something like a mishap investigation, it could easily be calculated from others. If you need to assign a name I would consider "Velocity", "Magnitude", "Earth-speed", or a proprietary defined acronym like "VVGS" (Vertical Velocity plus GroundSpeed). Just avoid "air" unless that's what you actually mean...

Answer 3

Typically it is the Inertial based systems that give us this kind of data. A GPS with a suitable computing module could provide the same thing.

The closest thing we have is called the FPV, Flight Path Vector or the 'Bird'.

In the cockpit, generally, the FPV provides the pilot only a part of the information, and displays it in a particular manner, vertical path and Lateral path being separately shown.

The actual 3D speed component is not one of them, and neither would the 3D Speed be of direct value in flying, or navigating the airplane.

Typically it gives us:
(i)the instantaneous Track and Vertical angle of the actual flightpath with respect to the earth, ie the ground,
(ii)also often, it gives use a projection of where the airplane will be in 10, 20, and 30 seconds based on the current instantaneous flightpath.
(iii) resolving the East/West and North/South vectors gives us the instantaneous Track and Groundspeed.
(iiii) resolving the Vertical component of the FPV gives us the Vertical Speed, though it is normally only used to validate the Air Data based Barometric VertSpd, VS.

None of these systems actually measure any Airspeed. They measure GS, Ground Speed, though strictly speaking, it could not be called an act of measurement, but something arrived at by using position data, ie Lat/Long at suitable intervals and computing the difference to give an accurate estimation of Ground Track and GS (=TAS in still air).

The plethora of acronyms related to speed, direction, and vertical disposition were necessitated due to way we physically measure, then compute, then display them and our basic flying skills have developed around these - IAS, CAS, EAS, TAS, GS, ALT, FL, TRK CRS, HDG(M), HDG(T), ATT. There's no point introducing new measures such as 3D speed, though I'm guessing your intent maybe to have "one speed to rule them all" along with a suitable depiction of airplane and flightpath in a 3D EVS (Enhanced Vision System).