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Nexrad display inaccurate |
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310pilot 
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Joined: 13 Apr 2015 Location: Louisville, KY Status: Offline Points: 102 |
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 Topic: Nexrad display inaccuratePosted: 01 Jul 2016 at 4:10pm |
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Has anyone noticed this? The image below has the SAME weather feed from WSI. The IFD depicts it with less contouring and shows the weather to be more intense. The mx20 (pictured right) shows less intensity and more contoured weather (better looking depiction also). In looking at the weather visually and other adsb weather products the MX20 is a way more accurate display of the actual weather.
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Catani
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Posted: 03 Jul 2016 at 12:37am |
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Taking into account the size of the image on the IFD is smaller than the MX20, it appears to me that the outlines of the weather appear to be close to identical, as well as the outlines of different intensity areas, with perhaps a bit of computerized smoothing of the pixels on the IFD (guessing perhaps due to a somewhat different data protocol from WSI for each box?). As far as I can tell, the only significant difference is the choice of colors for the intensity depictions.
It looks like they both use light green for the least intense, while after that colors differ. (Page 3-17 of the IFD manual has a picture of the colors for 4 levels of intensity displayed on the IFD: green, yellow, red, purple.) On the right, the next step up is colored dark green, whereas on the IFD it's yellow. Next step up after than is yellow on the right, red on the left. I assume the next level up on the right would be red, and purple on the IFD, which the weather on this day was not intense enough to display those colors. Does the MX20 have more than four levels? If not, that should cover it. If you're OK with flying into dark green on the MX20, you should be equally OK with flying through the yellow on the IFD.
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teeth6
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Posted: 03 Jul 2016 at 9:13am |
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Catani is correct. You need to check to see the colors used to depict the different decibel levels of return for the different providers. The decibel level that the MX20 depicts in yellow is the same decibel that the IFD depicts in red.
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310pilot
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Posted: 03 Jul 2016 at 9:28am |
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Thanks guys!! I think you are 100% correct. Avidyne uses different color intensities and smooths out the pixels a little....
Maybe it's just the Internet weather sites I use but the mx20 seems to more closely parallel those preflight sites than the increased intensities colors of the IFD. One would think there would be a standard when it comes to what colors to use. |
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310pilot
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Posted: 03 Jul 2016 at 1:31pm |
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Don't know how many of you use Intellicast....But look at the range of colors it uses to depict radar intensities ... I would like to see the IFD use more than just four colors for a more accurate picture,
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MysticCobra
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Posted: 03 Jul 2016 at 11:40pm |
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The ADSB data only include four intensities. Any additional colors the IFD shows would be interpolated, and not real.
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310pilot
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Posted: 04 Jul 2016 at 12:15am |
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Good to know. Thanks! The example I gave was with WSI inflight however and they have the ability to provide more colors.
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310pilot
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Posted: 04 Jul 2016 at 8:59am |
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Thank you again for everyones discussion on this. Below is a picture of the the same weather depicted on an iPad and the IFD. Now the iPad weather is from a different source (ADSB) than the IFD (WSI), so the picture will be a tad different..... however, note that foreflight on the iPad has "dark green" in their radar solution.
I firmly believe there needs to be a "standard" in depicting weather. It just does not appear the Avidyne took advantage of using "dark green" like seems to be the standard everywhere else. And while this seems like a small problem (just get used to the yellow....) it really has greater implications..... (" I flew into the yellow on the IFD so Im going to on this other weather system.....BAD IDEA!!!). Avidyne please consider incorporating dark green into your nexrad display.  |
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BobsV35B
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Posted: 04 Jul 2016 at 12:09pm |
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Could it be that we are trying to put more into our interpretation than there is knowledge to be interpretted?
Back before we had weather RADAR, we flew through a lot of stuff we would not fly through now. I am not saying we should change our thoughts about where we want to fly, but there is a lot more to interpreting todays weather RADAR than just looking at the colors on an individual screen. Do we have any idea as to how long ago each of the pictires shown had gotten their repective signals? There is a delay to each. They are not showing current weather!! Could be as much as fifteen minutes difference. |
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Old Bob, Ancient Aviator
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brou0040
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Posted: 04 Jul 2016 at 1:10pm |
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Would there be 15 minutes between the two displays when they come from the same weather source? You've got a valid point, but I believe it to be off topic. I agree there should be a standard. Without a standard, I'm not sure I'd put my vote behind Avidyne changing their color scheme to match someone else's. Which other source would they change to? Foreflight, Garmin, etc??? If they change, then suddenly people could be flying into weather worse than they expected because you downgraded the color intensities they have gotten used to with the Avidyne system. I say change to a standard if/when there is one and make sure people fully understand it has changed - and not until then. Just my 2 cents.
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ddgates
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Posted: 04 Jul 2016 at 1:17pm |
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This (ADS-B) and FIS-B weather were all driven by the government.
The GA sector has done miserably in standardization. Capstone? I cannot believe that such variances would be accepted in part 135. The value of standardization is no less valid for GA as compared to commercial...
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David Gates
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BobsV35B
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Posted: 04 Jul 2016 at 1:47pm |
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Standardization is the mortal enemy of innovation!
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Old Bob, Ancient Aviator
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AUXAIR
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Posted: 04 Jul 2016 at 2:30pm |
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"A foolish consistency is the hobgoblin of little minds"....
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David E.
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AUXAIR
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Posted: 04 Jul 2016 at 2:47pm |
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If you are seeking standardization, one other color disparity is that some systems indicate flight conditions for VFR in green, some in blue. Following that, marginal VFR is blue, or maybe green....
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David E.
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310pilot
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Posted: 04 Jul 2016 at 4:26pm |
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Yeah AuxAir, that one bothers me too!! I agree the only standard in GA is that there isn't a standard!! But in this case it seems like everyone else for NEXRAD uses Light Green then Dark Green, where as for some reason Avidyne chooses not to use Dark Green. Am I over simplifying the problem?
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paulr
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Posted: 05 Jul 2016 at 12:22pm |
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There's a specific requirement for certified ADS-B In systems to use those particular colors for flight conditions... even though a) they don't seem intuitive (cyan means VFR but green means MVFR?) and b) they don't match what the tablet software guys have done.
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AviJake
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Posted: 10 Jul 2016 at 10:19am |
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I'll look again to verify but if memory serves, it can be said that Avidyne is actually one of, or the only ones, who are actually complying with the FAA MOPS for such intensity color coding and color selection.
We've had to answer the same observations multiple times in the past so I need to dig up that homework and original design description data to cite the guidance in the area and our implementation details/compliance with such guidance. |
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Steve Jacobson
sjacobson@avidyne.com |
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AUXAIR
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Posted: 10 Jul 2016 at 12:07pm |
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The RTCA Minimum Operational Performance Standards for FIS-B only show four levels and three colors for depiction of radar reflectivity values, that I can find. They go from no color at less than 20dBz, to green at between 20 and 30 dBz, to yellow between 30 and 40 dBz, to red over 40 dBz. There may be other documents that apply, but I found these in the testing procedures in DO-358. Edited by AUXAIR - 10 Jul 2016 at 12:09pm |
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David E.
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AviJake
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Posted: 10 Jul 2016 at 12:42pm |
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Sure but our datalink MOPS compliance pre-dates ADS-B FIS-B systems by over a decade.
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Steve Jacobson
sjacobson@avidyne.com |
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Catani
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Posted: 18 Jul 2016 at 3:54pm |
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Foreflight 7.7 is out, and includes options to display weather in "standard" four-color "RTCA" colors: green, yellow, red and magenta. Just like the IFDs. See:
https://blog.foreflight.com/2016/07/14/logbook-flight-sharing-stratus-esg-support-new-radar-layer-in-foreflight-7-7/ https://blog.foreflight.com/2016/07/14/new-radar-layer-updates/ I guess this explains why Avidyne chose the colors it did. I don't understand why if a product is to display only four colors, why they also don't all chose the standard RTCA green, yellow, red and magenta. That would make everyone else's four colors the same as Avidyne's. I think using only RTCA's four colors falls a little short though -- it does not convey as much information as displays using more colors, or even as much info as old gray-scale analog weather radar displays. It also appears that ForeFlights standard weather depiction - what has been provided all along so far -- is of a higher resolution, and uses quite a few more colors. A good reason to continue to use ForeFlight or other similar app, it would seem at first glance, so as to extract as much info as possible from the data in the FIS-B transmission, which is not limited to four gradations. ForeFlight must have a reason for making the low resolution four color option available, but I don't see what it is.
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MysticCobra
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Posted: 18 Jul 2016 at 6:56pm |
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There are only four precip intensities delivered via ADSB, so only four colors required to display those intensities. Increased spacial or intensity resolution means more data to transmit. There is a tradeoff between RF signal range and data rate, and I'm sure that factored into the decision for how much resolution to provide.
Edited by MysticCobra - 18 Jul 2016 at 6:59pm |
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Catani
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Posted: 18 Jul 2016 at 9:21pm |
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Well, if you read the links I posted, one has a chart of the FIS-B intensities, and there are more than 4 listed on that chart. I'm going on a flight tomorrow and will take a look at ForeFlights standard high resolution radar mapping, and compare it with its new low resolution 4 color. Both displays will be derived from FIS-B input data, and it will be interesting to see how they differ in appearance, if at all.
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paulr
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Posted: 19 Jul 2016 at 10:03am |
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It seems like FF's downloaded radar imagery has significantly higher resolution than the datalink weather, at least from my casual eyeball inspection. There doesn't appear to be much difference in the resolution of datalink weather in FF (via a Stratus 1) and my IFD540 (via a Skytrax 100). I'll be interested to see your results. |
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MysticCobra
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Posted: 19 Jul 2016 at 2:40pm |
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Re-read the text above that chart. The NEXRAD radar system measuring precipitation intensity resolves to 8 levels of intensity (the left column, 0 through 7). However, that table explains how those intensities are reduced down to the 4 levels shown in the FIS-B display available via ADSB (the right column). Specifically, NEXRAD intensities 0 and 1 aren't displayed at all in the ADSB imagery. NEXRAD intensity 2 = ADSB Green. NEXRAD intensity 3 = ADSB Yellow. NEXRAD intensity 4-7= ADSB Red. (For others following along, the link Catani originally referred to is this one: http://blog.foreflight.com/2016/07/14/new-radar-layer-updates/ . The table in question is 2-3, at the very bottom of the page.)
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MysticCobra
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Posted: 19 Jul 2016 at 2:49pm |
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Yes, because the full NEXRAD data are easily available via a multitude of internet-based weather sources. But only a scaled-down set of radar data is broadcast via ADSB. All the ADSB receivers (Stratus, SkyTrax, or whoever) will be limited by that lower resolution ADSB data. Edit: I'm sorry; this thread started as a question about whether Avidyne is displaying the full resolution available via the WSI datalink feed, which is different from the ADSB feed. If that's the image comparison you're talking about, then I don't know what the WSI datalink resolution is compared to the original NEXRAD source it's derived from.
Edited by MysticCobra - 19 Jul 2016 at 2:55pm |
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Catani
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Posted: 20 Jul 2016 at 12:28am |
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Went on that flight today, and saw that inflight, ForeFlight does not make available the "lowest tilt," only composite. But the new feature allowing you to choose 4 color remains available in flight. I don't see much use for it.
And indeed, they are different. While ForeFlight's only source of weather data inflight is FIS-B, the difference between the standard display and four-color display are significant. The standard display has shades of green (light and dark), yellow, orange, red and magenta. Not sure if today's weather intensity was insufficient to create additional colors, or whether the boxes were tapped out at the red level. But I counted at least 6 shades of coloration on the standard FF display, derived from FIS-B. And I did take another look at the NEXRAD chart, and stand by what I said earlier. Levels 0 and 1 are considered ground noise and are not given a color by ForeFlight in either standard or four-color mode. Above that, I counted 6 more levels of intensity. It would seem the standard ForeFlight weather depiction uses all six levels, with a color scheme of its own design. Going "four color" option within Foreflight gets rid of the light green, and shows green, yellow, red and magenta. The result is a depiction that would lead you to think the weather is more difficult than it actually is. My conclusion: "four color": RTCA scheme is consistent with inexpensive weather radar boxes, but using that with ForeFlight to match up with your radar display would deprive you of addtional info.
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AUXAIR
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Posted: 20 Jul 2016 at 8:47am |
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In order to get a more complete understanding of the 4-color issue, there is a fuller explanation on the ForeFlight blog (emphasis added): "If you are flying with airborne radar, you may want to look at the new low resolution four-color NEXRAD mosaic ... The colors depicted in this radar mosaic match the standard color-to-dBZ mapping defined by the RTCA as documented in... [Standard DO267A]. This standard is also used for airborne radar displays. If you use ...(FIS-B) to receive weather while in flight... the four-color radar mosaic provides a much more ominous depiction of the weather as compared to its higher resolution counterpart... The reason for this may not be obvious. The data broadcast for FIS-B radar does not specifically include the raw dBZ values. Instead it uses intensity encoded values or “bins” that map to dBZ ranges.... Notice the wide 10 dBZ ranges for intensity encoded values of 2 and 3. Based on the RTCA standard... these are mapped in the ForeFlight four-color radar to green and yellow, respectively. Red is mapped to intensity encoded values of 4 and 5 with magenta mapped to 6 and 7. " So, unless you have a separate source of weather information (WSI, etc.) there are basic compromises in the lower-resolution display that are provided by FIS-B. But providing a "more ominous" presentation of the weather does not appear as a terrible compromise to me, given the basic limitations of delayed presentation of information. |
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David E.
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MysticCobra
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Posted: 20 Jul 2016 at 10:55am |
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Catani
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Posted: 20 Jul 2016 at 11:16am |
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Yes, as I see it that may be the main reason to use four-color on IFDs and the new ForeFlight low-resolution color scheme - so that your two sources of weather (NEXRAD and onboard) provide similar color schemes and weather depictions. For an experienced pilot, however, I would expect he would accept the limitations of his on-board weather radar and use it for the valuable tool it is, while preferring the added information provided by the high resolution six-color schemes provided by apps like ForeFlight, which use more of the FIS-B data information broadcast by the FAA.
I agree with the "more ominous" depiction of four-color compared to six color. It was this difference that caused the OP to post his message highlighting this difference. Switching back and forth between ForeFlight's high and low resolution NEXRAD displays sure made the weather look worse at the four-color low resolution setting. It's worth practicing this in flight so that you get accustomed to the difference. It is also this lack of information in four-color displays that made me miss the old analog weather radar cockpit displays that used an infinite number of shades of gray with no sharp edges. They provided much more information about the weather ahead than did four-color digital displays. But for new pilots, the four colors allowed them to skip the learning process involved in gray-scale displays. And for good technical reasons as well, those old gray-scale radars went West.
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BobsV35B wrote: