Aircraft monitoring…with a twist…or maybe a “shift”.

[Token]

First, let me say I am not 100% sure this should be in this forum, possibly it belongs more in Off Topic Wireless, if so I am sure Wayne will hook it up.

Although I am primarily an HF monitor (both for aviation and other things) I do occasionally delve into other bands.

First, a picture:

What is going on in this image? Aircraft are in transit, most of them in this image probably to and from LAX or other airfields in the LA Basin. The curves and slopes are aircraft Doppler shifts of the carrier frequency represented by the solid straight line across the center of the image. The carrier is the ATSC carrier from Los Angeles KABC TV Channel 7, on 174.310 MHz.

The ATSC carrier is received on a radio with SSB capability, in this case an Icom R8500 in USB mode (any transmitted carrier at any frequency and from any source can be used, but to work best it should be an unmodulated or steady carrier, or a carrier with the modulation starting at least 1 kHz from the carrier frequency, if not the Doppler shifted signals can be difficult to separate from the modulation). The audio from the receiving radio is put into the sound card of a PC and an audio spectrogram program (in this case Argo 1.34) is used to show a waterfall of the audio spectrum.

As an aircraft flies through the air radio frequencies, from up and down the spectrum, are reflected off of its skin, identical in function to radar. Because the aircraft is generally in motion compared to the transmitter source the reflections are Doppler shifted. The magnitude (in frequency) of the Doppler shift is dependant on two things, the original carrier frequency and the target radial velocity to the transmitter. The higher the carrier frequency the larger the Doppler shift will be for a given radial velocity. The radial velocity is not, necessarily, the same as the true velocity of the aircraft, these two would only be equal if the aircraft was flying directly towards, or away from, the transmitter source.

Now, Argo is very simple to use for this application, but often has a limited bandwidth that can be displayed for useful waterfall scroll speeds and levels of detail. In the above picture example you can only see about + and – 53 Hz, meaning the target radial velocity must be no more than + and – about 90 knots (remember, radial velocity to the transmitter site, not real velocity of the target). And the time from one end to the other is only about 5 minutes 30 seconds of history.

Another example:

This one is done a little differently, using an SDR-IQ and SpectraVue on the IF output of the Icom R8500 instead of the audio. The advantage here is wider bandwidth and more adaptability of waterfall scroll speeds. This image shows 700 Hz of width and 30 minutes of history. 700 Hz means I can see Doppler shifts of up to + and – 350 Hz, or radial velocities of up to 585 knots. In fact the two tracks in the lower left corner of the picture are at that speed and increasing.

The relative differences can be seen in the following two images, the top one is in SpectraVuethe second in Argo. The white-bordered rectangle in the first image is the coverage area for Argo and you can see the same returns inside it as in the full Argo shot:

Sometimes I have been able to correlate Doppler tracks with aircraft by monitoring LAX. When LAX approach or departure control commands a course correction you can sometimes see the radial velocity track change. The same thing with speed changes, LAX might tell a flight to reduce speed to such-and-such and you can see the curve change with the speed change. And when LAX is turning everyone at the same point you can anticipate such changes for each aircraft, sometimes Iding many aircraft in a row.

Helicopters can sometimes be differentiated from other aircraft because the rotors have a Doppler frequency all their own (think about it, each blade has a separate and constantly changing radial velocity as it goes around and around), and you can see the modulation on the other curve.

I post this thinking that other folks interested in aircraft might like to take a stab at “monitoring” them a different way. I must admit, the use of the ATSC carriers is not my idea, Jon-FL in the #wunclub IRC channel suggested it to me. I have seen this affect before on HF freqs but it is infrequent, few and far between. I am fortunate that the geometry works well for me and the high traffic LA area, I am about 120 air miles from LA. Other areas might not show the level of activity that I see here.

T!
Mohave Desert, California, USA

 

[poltergeisty]

So the blue image is from audio output!? wow!

 

[Token]

So the blue image is from audio output!? wow!

Yes, the blue displays are from audio. The upper one is configured how I normally use it when using audio only. The radio is turned to USB mode, the radio is tuned 600 Hz below the center carrier frequency, and the audio (record output) is simply connected to the sound card.

The lower blue display is also derived form audio, but not it appears inverted formmt he upper display. This is because in order to use the SDR-IQ/SpectraVue combination to look at the IF, and to also have a usable audio offset for audio out I have to select CW mode on the R8500. Since the R8500 uses LSB mode to do CW the direction of Doppler shift is reversed. So the items int hat image that appear to be positively shifted are actually negatively shifted.

T!

 

[b52hbuff]

Reminds me of this...
Mobile telephone masts 'can detect stealth bombers' - Telegraph

 

[poltergeisty]

It's funny you mention this because I was thinking of just that when I read this post. But then I thought well, low observable aircraft have radar absorbing materials etc, just like what the article says. So I guess the Brits knew the flight path of a stealth fighter prior to finding out that the jet could be tracked by cell phone towers? One has to wonder how this (if it really works) would fare with the detection of the F-22 now that the F-117A is out of commission. And how about the B-2? High flying and faster than the F-117A if I recall. Can you believe that somewhere in the Balkans is a museum with one of our crashed F-117A fighter/bombers?

Wasn't about sixty years ago that the British had come up with radar to track incoming bombers?

 

[poltergeisty]

F-117 Crash- The truth is out - PPRuNe Forums <---- Bookmark this site. You'll need it when another crash happens. Trust me, the damn media use it. :lol:

You'd think they use Linux. :lol:

 

[Sporkupine]

Now that is super cool and interesting! I'm going to look into this stuff further. Also, you know what this reminds me of? The "waterfall displays" the sonar guys used to have back when I was underwater much of the time. Thanks for introducing me to something I've never seen before!

 

[poltergeisty]

I guess that's another way of seeing it. :lol:

 

[majoco]

Poltereisty said:

"Wasn't about sixty years ago that the British had come up with radar to track incoming bombers?"

IIRC it was about 1936 when they first started test TV transmissions from Alexandra Palace which is/was reasonably near to the then Croydon Airport. The receivers showed what we now know as aircraft 'flutter' where the picture has bright and darker lines vertically across the screen as the aircraft re-radiates the signal which cancels/reinforces the original signal as the path length changes the phase.

Some bright spark then thought that this could be used to detect aircraft, and the rest, as they say, is history......

 

[Token]

Poltereisty said:

"Wasn't about sixty years ago that the British had come up with radar to track incoming bombers?"

IIRC it was about 1936 when they first started test TV transmissions from Alexandra Palace which is/was reasonably near to the then Croydon Airport. The receivers showed what we now know as aircraft 'flutter' where the picture has bright and darker lines vertically across the screen as the aircraft re-radiates the signal which cancels/reinforces the original signal as the path length changes the phase.

Some bright spark then thought that this could be used to detect aircraft, and the rest, as they say, is history......

I think the British test you are thinking of was on February 26, 1935, and involved a BBC shortwave transmission, nothing to do with TV. And, it was not an accident, but rather a planned test (the “Daventry Experiment”) as part of the development of Chain Home.

Actually the use of radar or radar like principals go back far earlier than that.

In 1904 a German engineer, Hulsmeyer, was granted a patent on a proposed way of using radio wave reflections to help ships avoid obstacles.

Radar, and its military applications including the possible ability to detect aircraft in flight, was independently developed in several countries (America, England, France, and Germany leading the way, Japan, USSR, Italy and the Netherlands also playing the game) at about the same time, 1934'ish and a bit before. As early as 1930 the US (Lawrence Hyland, at the Naval Research Lab) had shown that aircraft could be detected. All of this in each country was the culmination of lots of proceeding work coming together when the technological curve was about right. British radar development proceeded a bit more rapidly than the others from late 1934 on for the simple reason that England saw itself under the immediate threat of war. America enjoyed the potential conflict being at arms length, and therefore development was less urgent although only very slightly lagging behind Englands.

In 1935 England set up their first experimental radar system of a type suggested by Watson-Watt. By 1936 they had learned enough from this that they proceeded to set up a system of 5 radars, each about 25 miles apart, in a pseudo-monostatic arrangement. By 1938 these 5 stations, what would eventually be the core of Chain Home, were complete and operational. These systems were fixed site, could not be moved, and could not be retasked. This fit the needs of the time as England expected attacks from a more or less known direction. That is, to detect flights of multiple aircraft at distance to give fighter command enough time to launch interceptor aircraft and defend against the threat.

In America the development proceeded more leisurely and with a different initial goal. Again starting about 1934 they started developing radar as a viable military technology. However since they did not have a fixed threat axis to contend with the emphasis was on portable, and stearable, systems. These true monostatic systems were, by nature, more complex (although smaller in size) than the systems initially developed by England. By 1938 (although some sources quote 1939), the same year the Chain Home system became operational in the UK, the SCR-268 went into initial quantity production in the US, it specificaly had first tracked an aircraft in very early Feb 1936. This system was designed to track aircraft and direct antiaircraft guns and searchlights. The final configuration of the SCR-268 began production at Western Electric in 1939.

The Germans were not idle during this time, and also developed some interesting radars. However, they never really grasped that it would be important to an integrated defense network, and so although several of their systems were technologically very advanced as a weapons system they simply did not mature as radar, and its use, did in the US and England.

Sorry, did not mean to get that long winded, radar is a hobby of mine.

T!

 

[majoco]

Token, you are right. I obviously recalled incorrectly! Interesting experiments here:

Re: How to display radar (including diffraction/reflection) experimentally

Cheers - Martin ZL2MC

 

[Token]

F-117 Crash- The truth is out - PPRuNe Forums <---- Bookmark this site. You'll need it when another crash happens. Trust me, the damn media use it. :lol:

You'd think they use Linux. :lol:

You will probably never have to worry about an F-117 crashing again, they are retired and in “recallable storage”. And, I rather doubt there were any Windows products used in the aircraft, or Linux either .

Reminds me of this...
Mobile telephone masts 'can detect stealth bombers' - Telegraph

It's funny you mention this because I was thinking of just that when I read this post. But then I thought well, low observable aircraft have radar absorbing materials etc, just like what the article says. So I guess the Brits knew the flight path of a stealth fighter prior to finding out that the jet could be tracked by cell phone towers? One has to wonder how this (if it really works) would fare with the detection of the F-22 now that the F-117A is out of commission. And how about the B-2? High flying and faster than the F-117A if I recall. Can you believe that somewhere in the Balkans is a museum with one of our crashed F-117A fighter/bombers?

There is not a crashed F-117 in a museum in the Balkins…but there is a shot down one with pieces in several museums in multiple countries (of course, I am being intentionally dense, and I know what you meant, sorry, just had to get a shot in there ). And the best public data would seem to indicate it was shot down by an older SAM type, but the details of the event are simply not in the public record. It happened, no doubt, but the people who know about why and how are not talking.

People always forget several really important things about stealth and low observable technology. Stealth has never been claimed to (by anyone who has a background in the field) and does not make an aircraft invisible. It merely makes it much more difficult to see/detect/track. And detecting is not the same as tracking with a weapons system. The idea is that by the time you can see it the weapon from it is already on its way to you. Stealth reduces the range a target can be detected at, it is not a Klingon Cloaking device making it invisible.

So, lets say that the stories of cell towers and TV stations (VHF and UHF frequencies) being used to “track” stealth are correct, a technique that has never been proven to work by the way with combat configured aircraft, but is theoretically sound. Note that the article quoted does not mention a detection range, but speculates, baselessly I might add, that it could be as much as 15 miles. The type of data that can be derived from such low quality track information cannot be used to shoot at an aircraft, only to know it is in the air. Of course, knowing it is there is a portion of the battle….but not the important portion.

Tracking systems, that is systems that are used to guide weapons to the aircraft to kill it, tend to operate at higher frequencies, shorter wavelengths. In fact, not tend to, absolutely do today.

It has been 60 years, or more, since a shooter or director of some kind has operated at VHF or UHF frequencies. The reasons are many, and for the most part simple. Lets take the most basic reason of all, the small size of the weapon. Even a large anti-air missile (either surface-to-air or air-to-air) has a frontal cross section of probably less than 24 inches in diameter (larger is naturally possible, but none that I know of are in current use). This means that an antenna covering the whole frontal section of such missile cannot have more than a 24 inch antenna aperture, and most are going to be a good bit smaller than that. For a fixed size antenna gain goes down as frequency goes down. At 750 MHz a 24 inch dish would have about 10.5 dBi of gain and, more importantly, a beamwidth of over 50 degrees. It is kind of hard to develop tight track error information from such a wide beam. Meaning the missile would be lucky to hit the broad side of a barn…and a barn that was not maneuvering or employing any countermeasures to defeat the missile.

Now, take the same 24 inch diameter and do the math for radar X band, 8 to 12 GHz. Lets just take the center at 10 GHz. The gain is now up to a possible 33 dBi, and the beamwidth is down to less than 4 degrees. Using a simple monopulse comparator to derive track data you can expect usable track errors of maybe as little as 2 milliradians, and quite possibly a bit better.

Also, lets consider RCS.

RCS (radar cross section) is related to frequency. You have an RCS, your car has an RCS, aircraft have RCS’s, etc, every object that reflects radio energy has an RCS (and that means everything has an RCS, since everything reflects RF to some extent). RCS is, essentially, how well an object reflects energy. This is a combination of what the reflective surface is made of (how well it reflects), how large the surface is, and the shape of the surface. The physically larger it is for a given percentage of reflection and shape the larger the RCS. So, bigger means more RCS and more reflective means more RCS. But, a given size object (any shape other than a sphere) reflects more energy as the frequency of the RF goes up.

For example a square plate, with its reflective surface pointed directly towards the RF source (orthogonal to the source), the plate is 1 meter on a side and made of something that is highly RF reflective, lets say aircraft aluminum. The physical area is one square meter. But, the RCS at 1 GHz (1000 MHz) is 139.6 square meters. The RCS at 10 GHz (10000 MHz) is 13962 square meters. This means the amount of reflected energy, in a none stealthy target, goes up as frequency of the radar goes up. This is called RCS gain, or gain of RCS. Again, working in favor of shooters being at higher freqs.

However, you mentioned radar absorbent materials (RAM). RAM works to reduce the reflectivity of a surface, and simple RAM is easier to make the higher in frequency you go to a certain point. In fact, this out paces the increase in RCS gain from frequency increase. So, where you might have 20 dB of gain by increased frequency you can have a lot more reduction by RAM. Of course, I have been talking about basic RAM, materials you can by commercially for any anechoic chamber application, really cutting edge RAM coating design is going to be a closely guarded bit of information, so no idea what is going on there.

This MIGHT indicate that at lower frequencies, such as VHF and UHF used by cell towers and TV transmitters, could be less well controlled by RAM, but also will reflect less energy due to RCS gain.

So, could such systems work against stealth? Sure, it is possible. However, will such a system be able to track a stealthy object at usable ranges? Unlikely, at best. And, as I have stated, such systems cannot be used to shoot down a target, just to detect that it is in the area. The shooters still cannot track the target until it is very, very close. And it is likely the shooter will be dead before the aircraft is that close.

T!

 

[CalebATC]

At 15 miles, it could already be too late, also, depending on how high, fast, what types of bombs, etc.

I do have a question for you T- Radars in the F-15 (And other aircraft) have a frequency switcher on their radar. It can be selected for MED/HI(GH), MED, or HI(GH). Newer AESA's may have different settings, this is with the standard APG-63. So since you seem to know alot about this, how much do the frequencies vary? During head-to-head ops, you use high frequency radar, and for low speed closure rates (chasing aircraft, etc) you use medium frequencies. Why is that?

 

[poltergeisty]

From what I gather it would have to do with precision. The lower frequencies have a larger area they can cover as explained. Once your in close you switch to the high freq.

It's amazing technology, radar is. You use it for GPWS, to Secondary Surveillance Radar, and upon that you have ADS-B.

 

[guitarbrian30]

WOW or cool

WOW I am impressed... Living in an area know as fly over country South Dakota!

I love listening to the avation chatter. Now you can see the radar so to speak.

I have a new interest for the next year! Thanks for posting! I look forward to your next project!

 

[Token]

At 15 miles, it could already be too late, also, depending on how high, fast, what types of bombs, etc.

Well, one consideration might be that the range is not 15 miles from the aircraft to a target point, but 15 miles from a cell site. In that case, since cell sites or other signal sources can be much closer together, this could give potentially continuous coverage.

But there are a lot things that article is not saying. For example it takes energy from at least two transmitter sites reflecting off the target to be usable. And the “might be as much as 15 miles” that is quoted is completely baseless. By their own words they said that range based on how far a cell phone can talk to a site, and that simply does not matter in the least for this application. They are using reflected cell site energy from the surface of the aircraft, much like I was using reflected TV transmitter energy, except cell sites have a much lower ERP than TV transmitters.

I do have a question for you T- Radars in the F-15 (And other aircraft) have a frequency switcher on their radar. It can be selected for MED/HI(GH), MED, or HI(GH). Newer AESA's may have different settings, this is with the standard APG-63. So since you seem to know alot about this, how much do the frequencies vary? During head-to-head ops, you use high frequency radar, and for low speed closure rates (chasing aircraft, etc) you use medium frequencies. Why is that?

Hmmm…you have to be careful with the term “frequency” here. Let me preface with saying I have no first hand knowledge of the F-15 radar, I have never worked on one. I have worked on and used several other radars on aircraft, but I will not talk about those specifically. And this discussion could get really long, we need to talk about why one might change frequencies on a radar.

Radars are often fairly narrow banded and seldom have the ability to change the carrier frequency of their transmissions by as much as 10%. What that means is that if a radar is X band (8 to 12 GHz) it probably only has a frequency range that it can be retuned across of 1 GHz or less. Say 9.5 to 10.5 GHz. Some radars, particularly ones using solid state or TWT based transmitters can be wider. But still if it is X band it will be X band, not X and C band. To achieve multi-band capability typically requires a separate transmitter and sometimes a separate antenna for each band. You don’t find that very often in airborne platforms, where space and weight are at a premium.

And changing from the bottom edge of X band to the top edge of X band really does not change the way the radar works. You need bigger swings in frequency to get into the differing characteristics of the differing bands.

Why change bands in the first place? Because higher frequencies, from a single fixed size antenna, mean tighter beamwidths, and a more accurate track. It also means higher gain from the antenna, but higher freqs also have higher space loss, so this is not a big plus. The tighter beamwidths are the biggest single player, it helps you with track accuracy and to fight such problems as jamming.

In this traditional radar application High, Medium, and Low, even when followed by the term “Frequency”, would have a meaning that probably does not mean the carrier frequency of the radar, but rather means the Pulse Repetition Frequency (PRF) of the radar.

The PRF of a radar is simply how often it sends out a pulse, often expressed as a frequency. A radar that pulses 10 times a second is said to have a 10 Hz PRF. One that pulses 1500 times a second is a 1500 Hz PRF. 10,000 times a second is 10 kHz, etc. Remember that a radar sends out a relatively short duration pulse, and then listens for a while for the pulse return, echo, from the target. So, (pulse – listen), is one cycle, (pulse – listen), is the next cycle, rinse and repeat for each cycle. The range to the target is determined by measuring the time the pulse (echo) takes to return, dividing that time by 2 for one-way time, and then dividing the time by the speed of light. One nautical mile equals 12.36 microseconds of two-way time, thus 12.36 microseconds is called a “radar nautical mile”. 6.66 microseconds is a “radar kilometer”.

As you increase the PRF on a radar you increase, among other things, the average power returned from a target. You are also increasing your target update rate. You are increasing your overall track quality. So, higher PRF = better track, something very desirable in a rapidly changing situation such as closure of two aircraft or during or in close ACM.

Since High PRFs are so good, why don’t we just use it all the time?

A High PRF means a high cycle rate, and also means a shorter listen time. Remember that the radar detects its target during its listen time. If the listen time is too short and you make a 2nd pulse before pulse number 1 is returned from the aircraft the return becomes “ambiguous”. The return might be covered up by the next or some following pulse, but for sure you can not easily tell what transmit pulse the return pulse is associated with, so you do not know the range to the target. Yes, there are pulse coding methods that can make this nth time around return usable, but lets not go there.

A radar that is sending out a pulse 50,000 times per second has a listen time of 20 microseconds. If you divide that by 12.36 you will see that a radar with a 50 kHz PRF can only see targets inside of about 1.62 nautical miles maximum. A radar with a 10 kHz PRF has a listen time of 100 microseconds, and can see out to about 8.1 nautical miles maximum. And a radar with a PRF of 1000 Hz can see a target out to about 81 nautical miles maximum. I have left out a couple of other things, like required radar processing time and the transmit pulse duration itself, these will impact the maximum range a small amount.

So you can see that we would want to pick the PRF, or “frequency” to best match our anticipated needs. Give us the best track possible without having target off the end of our world. “Off the end of the world” is an informal term used to indicate that a target is beyond the range of your currently selected PRF.

Enter a truly modern radar, like the APG-70 or the later variants of APG-63 AESA. You asked how much do the frequencies vary and I responded with a “traditional” radar answer, not much and frequency might mean PRF instead of RF. But, the APG-70 is sometimes listed as having a very wide RF range, one web site claims “8-20 GHz, I to J band”. I find that difficult to believe, but I understand why they might say such a thing. If a radar worked across the range of 9 to 14 GHz it would be in portions of both I and J band (I band is 8-10 GHz, and J band is 10-20 GHz) and I could see someone taking an “I and J band” band comment to mean 8 to 20 GHz. I would bet a smaller range that includes portions of both I and J band, but not all of either.

If so a system would be much more capable, it could combine broad RF bandwidth with transmitters capable of high duty cycle and "frequency" might mean more than one thing. It might indeed be able to benefit from the tighter beamwidths of higher frequencies and combine this with the benefits of higher PRFs. Take all that and add the ability of the phased array antenna so that it physically does not have to swing around to center targets and you get a radar that can jump from target to target rapidly.

You would use lower RF frequencies when you wanted a wider beam, and lower PRFs for longer range, such as to watch a group of aircraft at long range. When engaged with an in-close fast moving target you want the tightest beam possible, so higher RF frequencies. You also want the most returns from the target you can get, higher track quality and increased burn-through on a jammer, so you increase the PRF. Ground attack might want the tight beams of higher RF frequencies combined with medium ranges of medium PRFs and high paint rates of the phased array. And you could combine this last mode with a factor I never discussed, the pulse width itself and how that can be shortened to bring out more detail or lengthened to increase reflected energy.

And so you have selections for the operators, to optimize the radar for the needs of the mission.

T!

 

[CalebATC]

From what I gather it would have to do with precision. The lower frequencies have a larger area they can cover as explained. Once your in close you switch to the high freq.

It's amazing technology, radar is. You use it for GPWS, to Secondary Surveillance Radar, and upon that you have ADS-B.

Well, it mostly has to do with closure speeds. I forget, it's somewhere between 300-450 KIAS where you switch to high frequency. And all below closure speeds are medium frequency.

In these days, everything goes crazy without radars!

I couldn't imagine being a ground controller at Atlanta without having ASDE-X!!! Air traffic control without radar would be a mess these days. Look at Oceanic stuff and imagine a lot more aircraft than that, and even closer!

 

[Token]

From what I gather it would have to do with precision. The lower frequencies have a larger area they can cover as explained. Once your in close you switch to the high freq.

While this is quite likely true remember that the APG-70 and the later APG-63 use phased array antennas, you can change the beamwdith (always more wide) without changing the freq. So, they could have picked the highest freq and only used that, adjusting the beamwidth as needed. There is much more to this, think about the potential ability of a phased array to track multiple targets at a time. Then the higher freqs could give multiple beams with higher individual gain then would be possible at lower freqs.

T!

 

[Token]

Well, it mostly has to do with closure speeds. I forget, it's somewhere between 300-450 KIAS where you switch to high frequency. And all below closure speeds are medium frequency.

This is the "increased track quality" I was talking about. You go to higher freqs (both RF and PRF) to increase the number of hits per second on the fast closing target, so the target moves as little as possible between track updates.

T!

 

[CalebATC]

Wow! Thanks for the such detailed reply! So, I am assuming you used to be in the USAF working on radars?

I did look it up in a flight manual I have, and yes, you were correct. Just a little more detailed

That all makes sense. Thanks for all the clearing up and explaining in simple terms!

I also read this about the AN/ALQ-135

"AN/ALQ-135 ECM station
The AN/ALQ-135 internal ECM station entered service as an integrated element of the F-15 Eagle's Tactical Electronic Warfare System (TEWS), making the Eagle the first air superiority fighter designed from the start with internal space reserved for an active jamming suite.
The system is capable of producing both noise barrage and deception jamming signals to counter a variety of both fixed- and variable-frequency threat radars operating in the bands of 2 to 20 GHz (NATO E through J bands). The transmitting antennas provide 360&#61616; coverage for protection against radar guided "surface-to-air" (SAM) and "air-to-air" (AAM) missiles. The system features 20 re-programmable processors working in parallel, to ensure fast and flexible responsiveness to changes in the threat environment."

So that does make sense. Thank you very much sir!