//------------------------------------------------------------------------------
// getHeatSignature() - Get the heat signature
//------------------------------------------------------------------------------
double* AircraftIrSignature::getHeatSignature(IrQueryMsg* msg)
{
Player* target = msg->getTarget();
if (target != nullptr) {
IrAtmosphere* atmos = nullptr;
WorldModel* sim = target->getWorldModel();
if (sim != nullptr) {
atmos = dynamic_cast<IrAtmosphere*>( sim->getAtmosphere() );
}
unsigned int numBins = getNumWaveBands();
if (airframeSig == nullptr) airframeSig = new double [numBins * 3];
if (plumeSigs == nullptr) plumeSigs = new double [numBins * 3];
if (hotPartsSigs == nullptr) hotPartsSigs = new double [numBins * 3];
//double reflectivity = 1.0f - getEmissivity();
double lowerBound = msg->getLowerWavelength();
double upperBound = msg->getUpperWavelength();
if (atmos != nullptr) {
if (atmos->getNumWaveBands() != getNumWaveBands()) {
// warning message
}
}
// apparently no emissivity factor in these airframe signatures
getAirframeSignatures(msg, lowerBound, upperBound);
getPlumeSignatures(msg, lowerBound, upperBound);
getHotPartsSignatures(msg, lowerBound, upperBound);
const double* centerWavelengths = getWaveBandCenters();
const double* widths = getWaveBandWidths();
//double totalWavelengthRange = ((centerWavelengths[getNumWaveBands() - 1] + (widths[getNumWaveBands() - 1] / 2.0f))-(centerWavelengths[0] - (widths[0] / 2.0f)));
for (unsigned int i=0; i<getNumWaveBands(); i++) {
// determine if our sensor band overlap this signature band
double lowerBandBound = centerWavelengths[i] - (widths[i] / 2.0f);
double upperBandBound = lowerBandBound + widths[i];
if (upperBound > lowerBandBound && lowerBound < upperBandBound) {
// calculate how much of this wave band overlaps the sensor limits
double lowerOverlap = getLowerEndOfWavelengthOverlap(lowerBandBound, lowerBound);
double upperOverlap = getUpperEndOfWavelengthOverlap(upperBandBound, upperBound);
if (upperOverlap < lowerOverlap) upperOverlap = lowerOverlap;
double overlapRatio = (upperOverlap - lowerOverlap) / (upperBandBound - lowerBandBound);
// get our main signature piece - airframe
double baseHeatSignatureInBand = airframeSig[i*3 + 2];
//if (isMessageEnabled(MSG_INFO)) {
//std::cout << "For wavelength " << currentWavelength << " Airframe Heat Signature: " << baseHeatSignatureInBand << std::endl;
//std::cout << "For wavelength " << currentWavelength << " Plume Signature: " << plumeSigs[i *3 +2] << std::endl;
//std::cout << "For wavelength " << currentWavelength << " Hot Parts: " << hotPartsSigs[i * 3 + 2] << std::endl;
//}
// assume plume bins & hot parts bins are same as airframe bins, so we
// can re-use the same overlap ratios and fractions. If not,
// they will have to be separately calculated.
baseHeatSignatureInBand += plumeSigs[i*3 + 2];
baseHeatSignatureInBand += hotPartsSigs[i*3 + 2];
// if we have an atmosphere model, get the reflected solar radiation contribution
// Solar signature is solar value * reflectivity i.e. (1 - emissivity)
// use of reflectivity here suggests that this is solar radiation reflected from the target
// this now done in the atmosphere model, during query return processing
//if (atmos != nullptr)
// baseHeatSignatureInBand += (reflectivity * atmos->getSolarRadiation(centerWavelengths[i], (double) target->getAltitudeM()));
airframeSig[i*3 + 2] = baseHeatSignatureInBand * overlapRatio;
}
} // for loop over waveBand
} // if (target != nullptr)
return airframeSig;
}
// this is called by the IrSeeker in the transmit frame, once for each target that returns a query
bool IrSensor::calculateIrQueryReturn(IrQueryMsg* const msg)
{
Player* ownship = getOwnship();
IrAtmosphere* atmos = nullptr;
double totalSignal = 0.0;
double totalBackground = 0.0;
if (msg->getSendingSensor() != this) {
// this should not happen
}
if (ownship != nullptr) {
WorldModel* sim = ownship->getWorldModel();
if (sim)
atmos = dynamic_cast<IrAtmosphere*>(sim->getAtmosphere());
}
if (atmos == nullptr) {
// assume simple signature
totalSignal = msg->getSignatureAtRange();
}
else {
atmos->calculateAtmosphereContribution(msg, &totalSignal, &totalBackground);
}
if (totalSignal > 0.0) {
const double targetRange = msg->getRange();
const double rangeSquared = targetRange * targetRange;
const double reflectorArea = msg->getProjectedArea();
const double ifov = msg->getInstantaneousFieldOfView();
// The relevant amount of background area is the field of view multiplied by the range squared
const double backgroundArea = ifov * rangeSquared;
// The seeker detects by comparing the amount of signal present
// with the target to the amount of signal there would be without the target.
// The amount of signal with the target represents the signal power plus
// that part of the background radiation that is not blocked by the target.
// If the target is larger than the field of view than it is all of background
// power in the field of view. Use this as the default value.
// noiseBlockedByTarget is irradiance, in units of watts/m^2
double noiseBlockedByTarget = totalBackground * ifov;
// If the target is smaller than the field of view, it is the background power
// in the effective field of view represented by the target, i.e. the
// target area divided by the range squared.
if (reflectorArea < backgroundArea) {
// these two are equivalent
// noiseBlockedByTarget *= (reflectorArea/backgroundArea)
noiseBlockedByTarget = (totalBackground * reflectorArea) / rangeSquared;
}
// attenuatedPower is irradiance, in watts/m^2
const double attenuatedPower = totalSignal / rangeSquared;
// signalAboveNoise is the signal that the detector sees minus what it would see with
// only the background radiation, and is just the amount of power subtracted by how much
// background power is being blocked.
// = (attenuatedPower + totalBackground*ifov - noiseBlockedByTarget) - totalBackground*ifov
// signalAboveNoise is irradiance, in watts/m^2
double signalAboveNoise = attenuatedPower - noiseBlockedByTarget;
// only Contrast seekers take absolute value in this equation.
// Hotspot does not.
if (signalAboveNoise < 0.0 &&
(msg->getSendingSensor()->getSensorType() == IrSensor::CONTRAST)) {
signalAboveNoise = -signalAboveNoise;
}
const double nei = msg->getNEI();
// Determine the ratio between the signal above the noise as compared to the level of
// radiation that would create a response at the same level as the sensor's internal noise.
// if NEI is in watts/m^2, then SNR will be dimensionless.
// if NEI is in watts/cm^2, then need to correct by 10^4.
const double signalToNoiseRatio = signalAboveNoise / nei;
const double backgroundNoiseRatio = noiseBlockedByTarget / nei;
//double signalToNoiseThreshold = msg->getSendingSensor()->getThreshold();
// allow all signals to be returned; threshold test will be applied in process()
{
const auto outMsg = new IrQueryMsg();
outMsg->setTarget(msg->getTarget());
outMsg->setGimbalAzimuth( static_cast<double>(msg->getGimbal()->getAzimuth()) );
outMsg->setGimbalElevation( static_cast<double>(msg->getGimbal()->getElevation()) );
outMsg->setAzimuthAoi(msg->getAzimuthAoi());
outMsg->setElevationAoi(msg->getElevationAoi());
base::Vec3d los = msg->getLosVec();
{
// This is for non-ownHdgOnly-stabilized gimbal angles
base::Vec4d los0( los.x(), los.y(), los.z(), 0.0 );
base::Vec4d los_vec = ownship->getRotMat() * los0;
double ra = std::sqrt(los_vec.x() * los_vec.x() + los_vec.y()*los_vec.y());
double az = std::atan2(los_vec.y(), los_vec.x());
double el = std::atan2(-los_vec.z(), ra);
outMsg->setRelativeAzimuth(az);
outMsg->setRelativeElevation(el);
}
outMsg->setLosVec(msg->getLosVec());
outMsg->setTgtLosVec( -msg->getLosVec() );
outMsg->setPosVec(msg->getTarget()->getPosition());
outMsg->setVelocityVec(msg->getTarget()->getVelocity());
outMsg->setAccelVec(msg->getTarget()->getAcceleration());
double angleAspect1 = outMsg->getPosVec().y() *
outMsg->getVelocityVec().x() -
outMsg->getPosVec().x() *
outMsg->getVelocityVec().y();
double angleAspect2 = outMsg->getPosVec().x() *
outMsg->getVelocityVec().x() +
outMsg->getPosVec().y() *
outMsg->getVelocityVec().y();
outMsg->setAngleAspect(std::atan2(-angleAspect1,angleAspect2));
outMsg->setSignalToNoiseRatio(signalToNoiseRatio);
outMsg->setBackgroundNoiseRatio(backgroundNoiseRatio);
outMsg->setSendingSensor(msg->getSendingSensor());
// probably unnecessary - should be default val
outMsg->setQueryMergeStatus(IrQueryMsg::NOT_MERGED); // FAB
msg->getSendingSensor()->addStoredMessage(outMsg);
}
//else // FAB - debug
//{
// int x = 0;
// x = x +1;
// }
} //totalSignal > 0
// else // FAB - debug
// {
// int x = 0;
// x = x +1;
//}
return true;
}
