[OFFICIAL] What are Star Trek sensors really capable of?

[Darth Wong]

OK, as I still have long-term visions of someday updating major rather than minor sections of my sci-fi website, I thought I would try something new: a series of "official" threads where I ask for people to input their ideas of what a particular technical subsystem is capable of. This will then be used as reference for future discussions. If it works out, I'll eventually make a sticky listing the "official" threads for each subsystem (shields, engines, phasers, etc). Note that this is not just a listing of events (ie- a rehash of the canon database), and it should involve theorizing about what these systems are actually capable of.

Ground rules:

1. Any factual assertion must be backed up with the name of the episode from which the observation was derived, as well as useful descriptions (ideally including screenshots, although that is not a requirement).
2. Conclusions should be derived from observations (no pure speculation).
3. Posts not meeting criterion #1 and #2 may be deleted in order to preserve the integrity of the thread.
4. Since the thread is "official" and may be used for future reference or perhaps even linked as a reference from elsewhere, let's try to keep discussions on-topic and debates from becoming too acrimonious. If necessary, a debate may be split and a summary post put in its place.

So let's see how this works out. We'll start with sensors. From "Angel One" we learned that Federation sensors could detect the presence of platinum and locate it on an entire planet, because they did precisely that: they located a Federation citizen on the planet Angel One by tracking the small amounts of platinum in his gear, because the planet was mysteriously devoid of natural platinum for some reason. However, in "Survivors", Riker said that a starship once evaded detection by hiding in a Lagrange point, which seems absurd in light of the spectacular capabilities implied by "Angel One" (both incidents are already detailed in the Canon Database). Any ideas as to how one explains this? What can their sensors really do, and why would they be able to locate traces of an element on a planet while losing an entire starship that's sitting in plain sight?

Discuss, and keep in mind that other aspects of sensor behaviour are fair game for discussion as well.

[Ted C]

With regard to "Angel One", I can only speculate that the sensors can be tuned to actively scan for the emission spectra of a particular material. Presumably the ship aims a sensor beam at the surface that will reflect off platinum in a distinctive way. This was effective in "Angel One" because there was no native platinum (or, at least, no refined platinum on the surface), so the foreign platinum of the merchant's insignia stood out.

This particular sensing technique would not be useful for detecting ships. Presumably you could send an active pulse that would "light up" materials common in ship hulls, but if the beam has to be fairly focused, you would have little luck finding a ship in all of space. Furthermore, I got the impression in "Survivors" that Worf's failure to detect a ship floating in a Lagrange Point was a sign of incompetence: Picard, Riker, and Worf himself all seemed to think that he should have spotted a ship in such a location.

Furthermore, while the type of scan used to detect platinum in "Angel One" must have been able to detect a small object at a distance of thousands of kilometers, the same technique might not have been so effective at the greater ranges (hundreds of thousands of kilometers) that would likely be required when scanning space for ships.

Starship shielding or other field effects might also interefere with such a scan.

Basically, locating the platinum in "Angel One" was like using a metal detector to find a needle in a haystack. Similarly, a metal detector would not necessarily be as useful for finding a needle in a city park unless you already had a good idea where to look.

[General Zod]

Found this script, which should be accurate.

WORF
The away team has requested that
we scan the planet surface for
traces of platinum.

PICARD'S COM VOICE
Have Mister La Forge break fixed
orbit and initiate a search
pattern.

WORF
Aye, Captain.
(and:)
Geordi.

GEORDI
Search pattern initiated now.

From the dialog, Worf is saying they're just going to be scanning the surface of the planet itself, not the actual entirety of the planet. And going based on what Picard is telling them, they're starting up a search pattern, as opposed to scanning everything at once. It doesn't seem like there's any type of serious contradiction here.

[Ted C]

From Voyager's "Scorpion" part 1, we have the "skeletal lock" incident.

Voyager was unable to locate crew members on a damaged Borg cube due to interference from the Borg ship; they couldn't scan for them on the cube or get signals from their communicators.

Torres proposed using a "skeletal lock" to transport the crew members back to the ship. She was able to detect the minerals in their bones with the sensors, and use that data get coordinates for transport.

This seems similar to the "Angel One" incident: they were able to focus an intense sensor beam on a relatively small volume of space in search of particular elements or chemicals.

[NecronLord]

For The Survivors couldn't Riker just be clutching at straws? The ship was an illusion after all. What's baffling, is that he came up with this 'it was hiding in a lagrange point' thing before thinking of a fairly ubiquitous technology like the cloaking device, when trying to explain how it had appeared there.

Given the actual dialogue from the script;

PICARD
Where did that come from?

RIKER
Apparently it was riding a
Lagrange point behind Rana
Four's furthest moon.

Perhaps what Riker is trying to suggest is that the vessel had been minimizing its emissions by sitting at the lagrange point with most systems shut down and as it was behind the moon, the Enterprise wouldn't have seen it?

EDIT: It's possible for lagrange points to pick up asteroids and other inert asteroids - notably in the case of the trojans - perhaps Rana Four's moon has such debris there, and Riker presumes that the "husnock ship" had been hiding among this rubble, and read as a rock?

[Ted C]

RIKER
Apparently it was riding a
Lagrange point behind Rana
Four's furthest moon.

Perhaps what Riker is trying to suggest is that the vessel had been minimizing its emissions by sitting at the lagrange point with most systems shut down and as it was behind the moon, the Enterprise wouldn't have seen it?

While that's seems like a reasonable explanation, Riker's statement doesn't make sense. By definition, a Lagrange Point has to be between two massive bodies, so their gravitational forces can cancel each other. It's difficult to conceive of an orbital position for the Enterprise that would put it on the opposite side of a planet's farthest moon from that moon's Lagrange Point.

[NecronLord]

Unless I'm hideously mistaken, there is an L2 point on the far side of The Moon, with L1 being on the near side, L3 the opposite, and L4 and 5 (the trojan points) preceeding and following it in its orbit. They're not just the point where gravitational forces cancel each other out directly between two bodies, but rather where the gravitational pull of two objects, one orbiting the other, are equal upon a third object. They're not all that stable, though, and station-keeping is required for long term stabilities.

Here's a pic, though it reffers to the Sun-Earth system rather than the Earth-Moon one. So long as they're on the inside of the moon in question, the lagrange point on the far side should be invisible.

A JPL diagram of the Sun-Earth Lagrange system.

[Ted C]

The Lagrange Points mark positions where the combined gravitational pull of the two large masses provides precisely the centripetal force required to rotate with them.

So, I can see where L2 would be a feasible position in which to hide behind the moon. We've seen in other episodes that massive bodies blocking line-of-sight are a problem for Federation sensors.

[NecronLord]

Sitting at the L2 point, with minimal emissions and letting the other ship pass by might be a valid ambush tactic in some circumstances, provided the incoming ship doesn't have a line of sight at any stage, perhaps that's what Riker's thinking has happened there, then.

[Ted C]

Federation sensors can normally detect a starship travelling at warp speed from light-years away, as seen in "Transfigurations". This is presumably because warp engines normally lose a lot of energy into subspace, where such energy can propagate at superluminal speeds to be picked up by a subspace sensor.

Cloaking devices can apparently hide these emissions, allowing ships to remain cloaked at warp speeds, but they can be detected if they try to travel too quickly, as seen in "Tin Man".

[General Zod]

For The Survivors couldn't Riker just be clutching at straws? The ship was an illusion after all. What's baffling, is that he came up with this 'it was hiding in a lagrange point' thing before thinking of a fairly ubiquitous technology like the cloaking device, when trying to explain how it had appeared there.

Aren't Klingons and Romulans the only major races known to use cloaking technology at this time in the series, though?

Perhaps what Riker is trying to suggest is that the vessel had been minimizing its emissions by sitting at the lagrange point with most systems shut down and as it was behind the moon, the Enterprise wouldn't have seen it?

EDIT: It's possible for lagrange points to pick up asteroids and other inert asteroids - notably in the case of the trojans - perhaps Rana Four's moon has such debris there, and Riker presumes that the "husnock ship" had been hiding among this rubble, and read as a rock?

Perhaps it's simply a sensor blind spot? The script in Angel One shows they had to do their sweep in a series of sections over the surface and didn't penetrate the entire planet. The S4 episode The Legacy shows that they have trouble scanning things to a certain point past the surface of a planet, so this holds up.

[NecronLord]

Aren't Klingons and Romulans the only major races known to use cloaking technology at this time in the series, though?

In other words, their two biggest and most notable neighbors? I don't see how that changes it from being bizzare that Riker didn't say 'cloak' when an alien ship appeared out of nowhere. I suppose that it could have come haring out from behind the moon to make him say that, of course.

Perhaps it's simply a sensor blind spot? The script in Angel One shows they had to do their sweep in a series of sections over the surface and didn't penetrate the entire planet. The S4 episode The Legacy shows that they have trouble scanning things to a certain point past the surface of a planet, so this holds up.

It's possible, though it makes slightly less sense that way. At least the 'magnetic pole' thing in The Legacy was... vaguely comprehensible, if as dubious as a receipt from a travelling market.

[Ted C]

Should this be a sticky?

[NecronLord]

Mike's quite capable of doing so if he desires. Anyway, I think it's safe to say that Federation sensors, from this are, at least in part, line of sight. Anyone know of any examples of them detecting objects in space withough a clear line of sight, on the far side of planets and things?

[Vympel]

From TNG "Parallels", the Argus Array, a "subspace radio telescope":



The facilities it can see are Deep Space 5 (top left), Iadara colonly (top right) Starbase 47 (bottom left) and Utopia Planitia on Mars (bottom right). For those that remember the episode, the Argus Array (previously featured in "The Nth Degree") had been retargeted by the Cardassians to observe Federation sites.

This Array is apparently 3LY or so from Cardassian space- anyone have any idea how far Cardassian space is from Earth's solar system?

[Chris OFarrell]

We also have in Unification a Federation starship on their side of the Neutral Zone being able to produce a passable picture of Spock on the Romulan homeworld with long range sensors.

Another instance I remember was in one of the final Voyager episodes that they were able to detect Talaxian life signs at around 4 light years, some colony on an asteroid powered by 'geothermal energy' (don't ask...just...don't).

[Alyeska]

Should this be a sticky?

Done

[Darth Wong]

The mechanism of elemental detection merits further examination. They must project some sort of radiation or field toward objects they wish to scan, and then detect its interactions with this field or radiation.

If we presume that this is probably "subspace radiation", to resort to treknobabble, it may have counterintuitive characteristics. For example, the fact that it may reflect from one element does not necessarily mean it will reflect well from others. This may explain why their sensors appear to be capable of penetrating deep through rock in some situations while reflecting from small platinum trinkets in others.

[Chris OFarrell]

The bolded section, "Taken on Romulus" is where my ambiguity lies. Obviously, the image is of Romulus (which, is the wording I would personally use to say the picture is of Romulus taken by a starship rather than "on"), but that could also be taken to mean a spy on Romulus took the picture with a long range telescope on the ground.

I'll investigate this and get back to you, but I'm sure they changed it in the episode itself to be a Starship scanning on the Federation side of the zone.

[Darth Wong]

The bolded section, "Taken on Romulus" is where my ambiguity lies. Obviously, the image is of Romulus (which, is the wording I would personally use to say the picture is of Romulus taken by a starship rather than "on"), but that could also be taken to mean a spy on Romulus took the picture with a long range telescope on the ground.

I'll investigate this and get back to you, but I'm sure they changed it in the episode itself to be a Starship scanning on the Federation side of the zone.

Which makes no sense, since they routinely speak of "visual range", and visual range is something you approach at sublight speeds. If visual range were measured in light-years, it would be ridiculous to approach it at sublight speeds.

[NecronLord]

I'm pretty certain that can be dismssed either as a gaffe, or just as laughable outlier. 'Visual Range' is a concept in Star Trek since the early episodes of TOS through to Voyager, and there's no other mention of such an implausible scanner.

[Darth Wong]

I'm pretty certain that can be dismssed either as a gaffe, or just as laughable outlier. 'Visual Range' is a concept in Star Trek since the early episodes of TOS through to Voyager, and there's no other mention of such an implausible scanner.

Especially when it's based purely on an interpretation of dialogue, and the predictions one could generate from this theory are so preposterously out of line with other observations as to be downright comical. I think people with no scientific mindset need to be reminded that a theory should generate predictions, and that those predictions should be at least somewhat compatible with observation.

[Ted C]

I think we've established that the ship's computer will construct visual representations of objects detected on sensors. Once it has enough information to identify a sensor contact as a Klingon K'Vort-class Cruisers, for example, it will use stored data to place a corresponding visual representation on the viewscreen (if desired). I'm not sure of the usefulness of such a feature, except perhaps to give the crew a visual concept to associate with sensor data; they might associate the visual with appropriate action more quickly than they would a written or spoken description.

"Peak Performance" demonstrates that this is a feature, and shows how it can be exploited by someone able to hack the system.

[NecronLord]

The only way it could possibly make any sense given the limitations known elsewhere are for the ship to be carrying some sort of super-duper interstellar sensor, like the smello-scope from Futurarama, or for them to have picked the image up in intercepted communications of the Romulans. I'd bet on the latter, given how many times a sensor like that would otherwise be useful.

As for the Argus array, can it be established that those things are actually being looked at in 'real time' and aren't just library pictures? I can call up pictures like those of the US on Google Earth, but it doesn't actually mean I've got access to sensors that can see them. Further, as the 'array' itself relays data, it's possible that it's part of a network, and the images being called up are actually being called up from remote locations by the Cardassians, rather than observed directly. Further, I'm not sure how you'd establish that 'Starbase Five' is any particular installation - I suspect Geordi may have read it off something, though - they've used that model dozens of times.

[Darth Wong]

Besides, the point must be made that if they can get sharp visual images from that far away, then their sensor range for basic detection of things like starships should be enormous because basic echo detection requires far less information than a visual, yet their sensor range seems to be similar to this range.