________________________________________ GURPS Vehicles 2nd Edition Additions MA Lloyd (malloy00@io.com) 9 August 1998 Modifications and Additions to Chapter 13: Sighting and Detection ________________________________________ p169 Active Sonar Modifiers. Recognition 'fish shaped' p171 Ladar Modifiers. Drop '(also reduces range)' under body of water, this is the same thing as the scan penalty. p173* Vision The Mk.1 Eyeball. Paragraph 2 "average spotting range" should be "maximum spotting range" and "beyond 2,000 yards" should be "beyond 200 yards." ________________________________________ This entire chapter should have been restructured to separate the general rules from the specific sensor implementations and modifier tables. I also wanted several significant rules changes. I would organize it: ________________________________________ Chapter 13: Sighting and Detection ________________________________________ [Introductory paragraph, from p168.] ________________________________________ 168a Kinds of Sensors ________________________________________ There are two general types of sensors: DD Line of Sight Sensors This type of sensor requires an unobstructed line of sight to a target to detect it, and is blocked by the horizon, terrain features, and in some cases even atmospheric conditions. See the specific sensor descriptions for details. A LOS sensor can only detect objects in the direction it is looking. Most sensors face forward and use the arc of vision on pB115; otherwise use the same arc, but center it on the side of the vehicle the sensor points out of. Sensors on turrets or rotating open mounts look in the direction the mount currently faces. Turrets or open mounts with nothing but sensors can rotate rapidly, effectively providing 360 degree vision. LOS sensors can be further divided into "active" sensors that emit some form of scanning energy - active sonar, radar, imaging radar, ladar - and "passive" sensors - vision, infrared, thermograph, passive radar - which do not. DD Indirect Sensors Indirect sensors are those that do not require an unobstructed line of sight, such as passive sonar, sound detectors, geophones, MAD, and gravscanners. Indirect sensors do not have arc of vision or line of sight restrictions, however they are not precise enough to generate images or be used as targeting sensors. Refer to the individual sensor descriptions for limitations on what they can sense. [The descriptions of sensors currently under this heading on p168 should be cut. To the extent they are true, they are already covered elsewhere] SB Navigation Any LOS sensor can be used to navigate in situations where vision is hampered e.g., by darkness or bad visibility. Indirect sensors are not accurate enough to be used for navigation on the ground, but may be adequate underwater, in flight or in space. SB Targeting Sensors [As Targeting via Sensors from p171, but replace the first 2 paragraphs with:] A "targeting" sensor is one precise enough to be used in place of normal vision when making ranged or melee attacks. Unless it has the No Targeting option, any LOS sensors is a "targeting" sensor. SB Horizon [from p168 maintext. By the way the actual formula is r (cos^-1(r/r+h1) + cos^-1(r/r+h2)). The current one is close enough] ________________________________________ p169a Sensor Performance ________________________________________ The primary measure of sensor performance is called Scan. Scan is added to detection rolls using the sensor to offset range or other penalties. Scan is based on the range of the sensor, as shown below: [Insert the Range to Scan Table and its following paragraph from p52 here] *Magnification:* Optical sensor descriptions often give a magnification rather than a range. Magnification is simply the range of the sensor divided by the range of unaided vision. To convert, multiply the magnification by 0.5 miles. [This replaces the Vision Bonus section on p50. Drop that table and the split bonuses and use the same rules as all other sensors] SB Expanded Speed/Range Table [from p168] ________________________________________ p169a Resolving Detection ________________________________________ DD Sensor Rolls [Important: omit the paragraph 'Range is the maximum...' It's false.] A character using a sensor is a "sensor operator." A character can only use a sensor controlled by his crew station, but can use sensors while doing other things, like driving or firing a weapon. A computer program can use any sensor datalinked to the computer. If an important object is detectable by a sensor, the GM should roll secretly to see if the sensor operator notices it. Any number of rolls can be made in a single turn of sensor operations provided they are to detect different targets. Add together the object's Size, Speed/Range, and Countermeasures modifiers, the sensor's Scan, and the sensor's unique modifiers (see sidebars) to get a net skill modifier. Scan [from p169] Size Modifier: [from p169] Range/Speed Modifier [from p169 but cut 'Underwater count every 5 yards...' Water penalties vary and are covered in the sensor descriptions] Special modifiers [from p169] Distraction Modifier: [from p170] Prior Contact: +4 bonus if the target is currently detected either visually or by another sensor on the vehicle (or by an ally using datalink to share sensor information), or if trying to "Improve Contact" as described under Improving Contact on p169a. Total the modifiers. If they add to -10 or less, detection is impossible: the sensor just isn't good enough, regardless of operator skill. Roll vs. the operator's Electronics Operation (Sensor) skill, apply the total modifier and read the degree of success from the Contact Quality Table below. SB Simple Detection If the total modifier is +10 or more, the GM can assume detection is automatic. If several allied sensor operators can detect the same object, the GM may wish to roll only for the ones who have the best chance of detection. It is also possible to skip the die roll altogether, simply compare the net modifier to the Contact Quality Table and use that as the result. E.g., a -3 or larger modifier would be "no contact". This gives the same result as an average roll against skill 10, and works well for NPCs. DD Contact Quality The degree of success of the sensor operation roll controls how much information is provided. Read the degree of success from the following table: Contact Quality Table Degree of Success Result Critical Failure Error -3 or less No contact -1 to -2 Contact 0 to +2 Detection +3 to +4 Recognition +5 or more or Identification Critical Success *Error* means the operator made a serious mistake. Some possibilities include 'detection' of something that isn't there, a wrong 'identification' such as positively identifying an allied vehicle as a hostile craft making an attack run, or miscalibrating the sensor (reducing its scan until it is re-calibrated). *No Contact* means the object is not detected. [then add the text from p170 omitting the first sentence.] *Contact* means the sensor operator notices something, but can't make out the details. This can be treated as a Detection result, but the GM distorts the details slightly. *Detection* means the object has been detected. This always provides a bearing and, depending on the sensor, sometimes a range, speed, and signal strength. For example, if an imaging radar detected Captain Morgan, the GM may describe her as "contact at six o'clock: small slow object 2 miles away." *Recognition* [from p171] *Identification* [from p171] SB Bearing [from p168] SB Signal Strength [Replaces Approximate Size from p169] Most sensors provide a "signal strength" determined by the skill roll modifier. If the skill modifier excluding modifiers for prior contact or distraction was -3 or less, signal strength is "very weak." If -2 to +2, it is "weak." If it is +3 or more, it is "strong." For sensors that return a range, the range penalty can be compensated to obtain an "approximate size". A suggested breakdown of approximations the GM can use to describe sensor contacts: [Use the ones from p169] Note that blip enhancers, radar reflectors and signature reduction countermeasures can result in "apparent sizes" that are not related to the actual size of the target. SB Improving Contact A sensor operator that has Detected an object, but has not achieved Recognition or Identification can try for it on later turns. This is treated exactly like a normal sensor skill roll, except that it gets the +4 prior contact bonus and minimum success is the previous result. For instance if the previous result was "recognition", the sensor operator was hoping for "identification," but even a roll of "no contact" remains "recognition." This does require an action. ________________________________________ p171a Countermeasures ________________________________________ DD Signature Reduction Signature reduction systems make the vehicle harder to detect. They include sound baffling, stealth, IR and emission cloaking, camouflage paint, chameleon systems and invisibility. The modifier for any of these system is applied to the Size modifier of the vehicle. This does mean the reported approximate size will be smaller than the true size, unless the operator obtains 'recognition' and corrects for the concealment system. DD Area Jamming Area jammers generate noise in an attempt to swamp the sensor signal. The jam rating of the area jammer is applied as a penalty to any sensor roll to detect anything inside the jamming field, or to any sensor rolls made by sensors themselves in the field. DD Breaking Contact [Note: substantial change to (2)] Once achieved, detection (and recognition or identification, as well) is maintained without need for any die rolls until one of the following occurs to "break contact": (1) the object moves out of line of sight or arc of vision, if that is a requirement (it isn't for indirect sensors). This is the easiest way to break contact. (2) the target does something that reduces the skill modifier to detect it -- moves away, turns off a blip enhancer, turns on an area jammer, etc. Immediately re-roll detection to see if contact is maintained. The +4 for prior contact does apply. If the modifier falls below -10, contact is automatically broken. (3) the target pulses an effective active jammer. Contact is broken unless the sensor operator makes a skill roll at a penalty equal to the jam rating of the active jammer (4) the target launches an effective decoy. Contact is broken unless the sensor operator makes a skill roll at -4. Effective decoys are: Chaff of the same or higher TL as a radar, imaging radar, ladar or AESA. Flare of the same or higher TL as an infrared, thermograph, passive radar, neutrino detector, or multiscanner in radscan mode. Sonar Decoy of the same or higher TL as an active or passive sonar. Note that smoke, hot smoke, prism and blackout gas do not count as decoys, but a thick enough cloud can block line of sight, automatically breaking contact. DD Spoofing [This is a major change in Spoofing, I think its a significant improvement, as it allows spoofed recognition and identifications, and eliminates the record-keeping step at the undefined 'end of the turn'] Spoofing is the sensor equivalent of an active defense. The sensor operator knows something is there, but is receiving multiple illusory targets and/or false information about the real one. Any time a sensor tries to obtain useful information about a target with an operating deceptive jammer, roll against its jam rating. If the roll succeeds, the information obtained is flawed -- 'detection' gives false bearings, attacks using targeting sensors automatically miss, guidance systems lock onto false targets, 'recognition' or 'identification' reports something other than what is actually there and so on. If used against a homing weapon, roll every turn to break the guidance lock. If it's important (e.g., for proximity warheads) assume deceived targeting sensors and guided weapons miss by 1/50 the total range or one yard, whichever is greater. SB Invisibility [from p174] But replace the first sentence with these two: Invisibility conceals the subject from sensors operating in the 'optical' region of the spectrum -- including ultraviolet, visible light, infrared and millimeter waves. An invisible object cannot be spotted visually, or by infrared, thermograph, passive radar, ladar or imaging radar, but standard radar can detect invisible objects. SB Signal Enhancement Anti-Camouflage consists of minor modifications that provide a +2 bonus to attempts to detect the vehicle. Examples include camouflage paint patterns in contrasting colors, flashing a small mirror toward an observer, or mounting a half wavelength pointed metal rod on the surface to reflect radar. Blip Enhancers (p.60) are active systems that duplicate or amplify a sensor signal, adding +1 to +4 to the effective size modifier of the vehicle carrying the blip enhancer. IFF/Transponders (p.57) return an identification sequence in response to an interrogation signal. Some units treat certain types of active sensor beams as an interrogation signal. Such sensors get a +4 to detect the IFF equipped vehicle. Those equipped with the proper IFF systems can display the response as a label on the sensor blip; those not so equipped see the transmitted information as part of the return signal and interpret the +4 as part of the target Size modifier. SB Force Screens and Detection [from p174, but add:] 'Since the screen blocks active sensor beams before they reach the vehicle, it negates any benefits of stealth or similar signature reduction surfaces against active sensors.' DD Handing Off Contact [Cut Duplicates Prior Contact under DD Sensor rolls] ________________________________________ p173a Sensor Modifiers ________________________________________ [A number of table entries duplicate existing rules, either from the headers or the specific concealment/signature reduction rules, which are best handled as a reference from the headers. These are cut. Information on flares and deceptive jammers is also be cut, as it does not agree with either the original rules or my modifications above.] CC Visual Sensors These rules apply to vision and LOS sensors operating in visible light, such as telescopes and optical imagers. Aside from the horizon and solid objects, LOS is blocked if the sensor is in total darkness, or if the target is concealed behind blackout gas, or 10 yards or more of thick smoke, or 50 yards or more of water, thick fog, snowstorm, cloudbank or dense forest or jungle, or 500 yards or more of mist, rain, snow, or light woods. Camouflage paint and Chameleon systems (p.91) can reduce visible signatures. DD Vision Rolls Use the rules for Sensors, but replace Electronics Operation (Sensor) skill with a Vision roll: that is IQ, modified by any advantage or disadvantage that affects normal vision, in particular Acute Vision, Alertness, and Bad Sight. The Scan bonus for normal human vision is +9 (0.5 mile range). Scan ratings for binoculars, telescopes and other optics can be found using the rules in Sensor Performance (p169a) SB Visual Sensor Modifiers [from p174] The Bad Light or Darkness note should read: There is no penalty to see an object illuminated by a headlight, searchlight, or its own running lights. The darkness penalty is halved if an object is silhouetted against something else, like the moon or a light source. Night Vision, or the Light Amplification option, also negates darkness penalties CC Infrared and Thermograph Sensors These rules are used by infrared and thermograph sensors, PESA operating in thermograph mode, and for infrared or imaging infrared guidance weapons. [use the text blocks from p169-170 beginning:] Aside from the horizon and solid objects, LOS is..... Detection gives a bearing and approximate size, plus a..... To the first add: IR Cloaking or Emission Cloaking (p.91) reduce IR signatures. If the target has both systems, use only the better modifier. Emission or IR cloaking has no effect if the object is using a reaction engine or a power plant with a hot exhaust. SB Infrared and Thermograph Modifiers Object is . . . . Silhouetted against clear sky: +2 Silhouetted against space: +24 (sic) Using a power plant: +3 log (kW output) Using a power plant with a hot exhaust: additional +4 Using a reaction engine with a hot exhaust: +3 log (thrust) +k. Where k is 2 if jet, 3 if chemical rocket, 4 if fission, 5 if antimatter thermal and 6 if fusion. Using TL9 reactionless thruster: +3 log (kW) Early TL7 IRH guidance systems do not get these bonuses and instead are at -7 if *not* aimed directly at the hot exhaust pipe of a jet, rocket engine, gas or MHD turbine, etc. Object is within, or line of sight passes through . . . . A body of water: -1 per yard. Blackout gas or hot smoke cloud: -1 per yard. Blizzard: -1 per 5 yards. Falling rain and snow: -1 per 50 yards. Light woods: -1 per 50 yards. Dense woods or jungle: -1 per 5 yards. Hot air above a fire: -1 per 5 yards. CC Passive Radar These modifiers are used by passive radars, PESA operating in passive radar mode, and for passive radar homing (PRH) weapons. Aside from the horizon and solid objects, LOS is automatically blocked by 5 yards or more of water or 50 yards or more of blizzard, dense forest or jungle. Emission cloaking (p91) is effective at reducing passive radar signatures. Detection gives a bearing and approximate size. Recognition means the object's shape stands out. Identification provides a sharp image. SB Passive Radar Sensor Modifiers Object is . . . . ...[use the IR modifiers above] Object is within, or line of sight passes through . . . . A body of water: -2 per yard. Falling rain and snow: -1 per 50 yards. Light woods: -1 per 50 yards. Blizzard, dense woods or jungle: -1 per 5 yards. Chaff cloud -1 per yard. CC Radar and Imaging Radar These modifiers apply to radars and imaging radars, to AESA operating in either mode, and to active radar homing or semi-active radar homing weapons. Aside from the horizon and solid objects, LOS is automatically blocked by 5 yards or more of chaff or 50 yards or more of dense woods or jungle. Stealth systems (p.91) are effective at reducing radar signatures. Detection gives a bearing and approximate size, range and speed. "Medium contact at 12 o'clock, range 2,000 yards, speed 1,200 mph." Recognition means the object's shape can be somewhat discerned: "contact is medium winged aircraft." Identification is possible only if using imaging radar. It provides exact size and a sharp image, though with no color or flat detail (so you can't read markings): "a sleek delta-winged single engine fighter, maybe a Mirage 2000." SB Radar and Imaging Radar Sensor Modifiers Air scan radar detecting target silhouetted against ground or water: -5 Surface scan radar detecting target silhouetted against sky or space: -5 Object is not silhouetted against sky or space: -4 (cumulative with above!) Object has . . . . Reflective surface: +2 Retroreflective surface: +10 Nonmetallic structure: use the size modifier of the largest metal part, or -6. Line of sight passes into or through . . . . A body of water: -6 per yard. Falling rain or snow: -1. Light woods: -1 per 50 yards. Dense woods or jungle: -1 per 5 yards. Radius of area jammer: -1 x (jam rating) Chaff cloud: -5, or -2 per yard, whichever is worse. CC Ladar These modifiers apply to ladar and to active laser homing (ALH) weapons. Aside from the horizon and solid objects, ladar LOS is automatically blocked by any prism or blackout gas cloud, 5 yards or more of chaff, 10 or more yards of dense fog or smoke, or 50 yards or more of cloudbank, mist, dense woods or jungle. Both TL8+ stealth (p.91) and chameleon systems (p.91), but not camouflage paint, are effective against ladar Detection, Recognition and Identification: identical to imaging radar. SB Ladar Sensor Modifiers Object is . . . . Silhouetted against sky or space: +2. Object has . . . . Reflective surface: +2 Retroreflective surface: +10 Line of sight passes into or through . . . . A body of water: -8. Thick fog or smoke: -1 per yard. Mist, cloudbank, falling rain or snow: -1 per 5 yards. Light woods: -1 per 50 yards. Dense woods or jungle: -1 per 5 yards. Prism cloud or blackout gas: detection fails automatically! TL8+ chaff cloud: -5, or -2 per yard, whichever is worse. CC Active Sonar These modifiers are used for active sonar detection (including air sonars) and for the attack roll of sonar guided weapons. Radical sound baffling (p.91) partially reduces sonar signatures. Detection gives a bearing and an approximate size, range and speed. Round range and speed to nearest 10 mph or 100 yards. "Medium contact 12 o'clock, range 2,000 yards, speed 40 mph." Recognition gives an accurate range, and the object's general shape is discerned: "contact is fish shaped." Identification is possible only if using imaging sonar. It provides exact speed and a sharp image, though with no color or flat detail: "contact is a Sperm whale." SB Active Sonar Modifiers Object is in, or line of sight passes through . . . . Trace or vacuum atmosphere: no detection! Density layer boundary (e.g. thermocline, halocline): -4 Object contains a density boundary (swim bladder, air filled space): +4 SB Air Sonar Modifiers These additional modifiers apply only to sonars operating in air, that is to active sonars with the air sonar option. Object is in, or line of sight passes through . . . . Light woods: -1 Dense woods or jungle: -2 Thin atmosphere: -4 Very thin atmosphere: -12 CC Passive Sonar Detection Passive sonar detects sounds produced by the target. Stationary targets with no internal moving parts or crew cannot be detected. These modifiers apply to passive sonar, active/passive sonar operating in passive mode or passive sonar homing (PSH) weapons. Passive sonar is an indirect sensor. In order to work, both the sensor and the target must be in the water. Note that unless the sonar is a towed array, a moving water vehicle cannot detect targets behind it using passive sonar. Sound baffling systems (p91) reduce the sound signature of the target. Size modifiers apply only to detect a target moving through the water. Detection gives a signal strength ...[from p172, but replace the last paragraph with the second paragraph under Passive Sonar on p52] SB Passive Sonar Sensor Modifiers Object is not in or underwater . . . . no detection Sensor is not in or underwater . . . . no detection Object is . . . . Not maintaining sound discipline: +2 Moving using flexibody, reactionless thrusters or TL7+ hydrojets: +0 Moving using TL7+ ducted propellers: +2 Moving using any other propulsion system: +4 Using any heavy machinery, including combustion engines: +5 CC Magnetic Anomaly Detection MAD sensors detect anomalies in the magnetic field caused by large ferrous objects or electrical currents. A nonferrous object not using any electrical or magnetic equipment cannot be detected! Size modifier is applied for the largest ferrous metal object aboard. All TL6- metal armor is considered ferrous as is cheap or standard armor at TL7, and cheap armor at TL8+. Emission cloaking (p91) reduces magnetic signatures. Detection: This gives the object's ...[from p173] SB MAD Modifiers Object has . . . . Magnetic Passivation: -2 Antimatter storage: +6 +1 per gram Fusion or antimatter rockets or air rams: +25 + 2 log[thrust] Superconducting power cells: +2 log(kWs stored) Electrical power generated or used: +2 log(kW) Powerplant is MHD, fusion or antimatter: +15** Mag-lev propulsion or MHD (TL8+) Hydrojets +30* Fired electromag (including gauss and railgun), flamer or fusion gun: +15* Any other magnetic technology: +15* * in addition to the bonus for electrical power used. CC Geophones Geophones are indirect sensors that sense vibrations caused by objects moving over or through the ground. A geophone must be stationary and in contact with the ground to pick up these vibrations. An object that is not moving, or not touching the ground, cannot be detected. Sound baffling is effective against geophone detection. Detection gives a bearing and signal strength only. Recognition provides some idea of what the target is (firing artillery, a tracked drivetrain in the 100 to 1000kW range, a lot of marching troops) Identification tells you exactly what is making the sound (its an M1A1 tank), and how far away it is to one significant digit. SB Geophone Modifiers Object is . . . . Walking or crawling slowly while successfully using Stealth skill: -1 x times the amount the Stealth roll made. Tunneling underground: +4. Object has . . . . Extremely low ground pressure: -2 Very low ground pressure: -1 Very high ground pressure: +1 Extremely high ground pressure: +2 Object drivetrain power is . . . . Under 10 kW: +0 10 kW or higher: +2 log (kW) CC Neutrino Sensors Neutrino detectors can pick up neutrinos emitted by nuclear powerplants (including fission, RTG, fusion, NPU, antimatter and total conversions systems), equivalent reaction engines, detonating nuclear explosives, stars and force screens. A target lacking such technologies is not detectable. At TL10+ Emission cloaking is effective at reducing neutrino emissions. Detection gives only signal strength and bearing. Recognition also determines the type of device generating the neutrinos Identification also determines the range, and provides details of the device (area and DR of screens, power output of powerplants etc.) SB Neutrino Detection Modifiers Neutrino emitting powerplant: +3 log [kW] Neutrino emitting reaction engine: +4 +3 log [thrust] Fission or radioisotope source: -4 Antimatter or total conversion: -2 Force screens: +6 + 3 log [kW consumed] Nuclear blast: +38 + 3 log [kilotons] Sun: +72 CC Gravscanners Gravscanners detect large masses and the use of gravity manipulation technologies. Objects with no grav technology and under 1,000,000 tons cannot be detected. TL11+ emission cloaking is effective against gravscanners. Detection: Reveals the object's bearing, signal strength, and speed to one significant digit: "weak signal at 3 o'clock, moving 50 mph." and if any form of gravity-manipulation technology is in use. Recognition: Reveals the object's mass and range to one significant digit, and what kind of gravity manipulation technology is in use. Identification: Reveals mass and range of object to two significant digits, and details (GM's option) of the gravity manipulation technology used. SB Gravscanner Sensor Modifiers Object masses . . . . 1,000,000 tons : +0 10 million tons : +3 100 million tons: +6 1 billion tons : +9 and so on Earth mass : +46 Solar mass : +63 Object is using . . . . Artificial gravity or G Compensation : +3 Contragrav propulsion: +6 Deflector screen or force shield: +9 Gravitic gun: +12 Gravity beam weapon, or is using a tractor or pressor beam: +18 Gravity-ripple communicator: -range penalty for the communicator range CC Multiscanners [While still implausible, with these changes multiscanners at least feel like something other than Seek spells] Multiscanners are advanced sensors that may operate in one of three modes. Emission cloaking is effective against all multiscanner modes. Radscan: This can be tuned to function as an advanced radar/laser locator (p59), a radio detector (p59) or energy scanner (treat as MAD except it can detect any kind of power plant). When functioning in radscan mode, a multiscanner does not emit any scanning radiation. Chemscan: The scanner can be set to detect specific chemical compounds or elements, e.g., TNT or steel. Roll to detect each concentration in range, using the size modifier of the chemical concentration, not the size of whatever is carrying it. If the target is not entirely composed of the chemical scanned for, roll at a penalty to scan: -2 if 10% or less, -4 if 1%, -6 if part per thousand, -12 if part per million. A chemscanner may also be used to determine the chemical composition of an object detected by other means. Elemental composition can be found to part per thousand levels automatically; further interpretation requires an operator or expert program with the Chemistry skill. Bioscan: As above, but optimized to detect life forms. Roll to detect all carbon-based life forms within range. Use the size modifiers for the individual life forms. It can be set to detect general categories (e.g. mammals) at -4, specific species (e.g., humans) at -8, or a particular individual at -12 if a person's genetic "fingerprint" is in a database linked to the scanner. Chemscan and Bioscan modes are active sensors SB Multiscanner Sensor Modifiers When using bioscanner or chemscan functions, use these modifiers: Target underwater: -1 per 2 yards of water. Target is behind a wall: -1 per 5 points of wall DR and HP. Target inside a sealed vehicle/robot or armor: -1 per 5 points of armor DR. Bioscanner vs. target concealed in vegetation: -1 per 10 yds of cover. Target wearing a distort belt or a holodistort belt: -2 x (TL-9) of belt.