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ADS-B Radar Colors - Foreflight vs. GRT

L

lr172

Well Known Member
I had an interesting experience coming back to Chicago last night. There was some rain and cloud cover in the Chi area. What was interesting was the significant difference in how the returns were colored in Foreflight vs the GRT unit. The data is coming from the same Stratux unit.

Foreflight showed the entire area in two, possibly three different shades of green with one spec of yellow. The GRT was showing similar coverage, but was shown as a 60/40 split of green and yellow with some small red areas. Due to the discrepancy, I called up FSS and asked for there interpretation of the radar and they called it "light to moderate returns." I flew between the returns and avoided most of the rain, but got close to the Green/yellow area and could clearly see that enough rain was falling to see it and reduce the ground visibility. It was night time, so hard to tell how much rain.

I suspect ADS-b is just sending DBz figures for each geographical sector or unit of resolution and each device is a applying the coloring based upon their legend/protocol.

I am wondering if others have seen this as well. I am most curious as to which coloring scheme most closely represents what I am used to seeing with internet-based radar tools, such as ADDS.

Larry
 
lr172 said:
I had an interesting experience coming back to Chicago last night. There was some rain and cloud cover in the Chi area. What was interesting was the significant difference in how the returns were colored in Foreflight vs the GRT unit. The data is coming from the same Stratux unit.

Foreflight showed the entire area in two, possibly three different shades of green with one spec of yellow. The GRT was showing similar coverage, but was shown as a 60/40 split of green and yellow with some small red areas. Due to the discrepancy, I called up FSS and asked for there interpretation of the radar and they called it "light to moderate returns." I flew between the returns and avoided most of the rain, but got close to the Green/yellow area and could clearly see that enough rain was falling to see it and reduce the ground visibility. It was night time, so hard to tell how much rain.

I suspect ADS-b is just sending DBz figures for each geographical sector or unit of resolution and each device is a applying the coloring based upon their legend/protocol.

I am wondering if others have seen this as well. I am most curious as to which coloring scheme most closely represents what I am used to seeing with internet-based radar tools, such as ADDS.

Larry
Click to expand...

I don't know the answer to your question, but I've come to the conclusion that any given product's "coloring" of radar returns must be taken with a huge grain of salt. I happened to have my Garmin 396, with XM weather, along with me when I drove through the worst thunderstorm I have ever seen. Absolutely torrential rain, copious lightning. The Garmin/XM never showed it any worse than yellow (and there wasn't much of that).
 
There is nothing I am aware of in the Capstone protocol description or associated specs that govern display of the data. Foreflight tries to conform to NEXRAD presentation from my observations, other products may (and are free to) do differently.
 
lr172 said:
I had an interesting experience coming back to Chicago last night. There was some rain and cloud cover in the Chi area. What was interesting was the significant difference in how the returns were colored in Foreflight vs the GRT unit. The data is coming from the same Stratux unit.

Foreflight showed the entire area in two, possibly three different shades of green with one spec of yellow. The GRT was showing similar coverage, but was shown as a 60/40 split of green and yellow with some small red areas. Due to the discrepancy, I called up FSS and asked for there interpretation of the radar and they called it "light to moderate returns." I flew between the returns and avoided most of the rain, but got close to the Green/yellow area and could clearly see that enough rain was falling to see it and reduce the ground visibility. It was night time, so hard to tell how much rain.

I suspect ADS-b is just sending DBz figures for each geographical sector or unit of resolution and each device is a applying the coloring based upon their legend/protocol.

I am wondering if others have seen this as well. I am most curious as to which coloring scheme most closely represents what I am used to seeing with internet-based radar tools, such as ADDS.

Larry
Click to expand...

There is a setting in FF which allows you to choose between 4 color radar and 5 color...as to how to match it up with nexrad, I don't know. Looks like there's some good info here: https://blog.foreflight.com/tag/weather. Look about 2/3s the way down on that page.
 
Interesting observation..

This doesn't answer your question but here is another data point to consider. At KOSH I was speaking to the IFlygps folks about how they render their radar images. I was curious in this day and age why some of the images you see on EFB Apps are pixelated while others have smooth boundaries. In brief I was asking him why they are painting blocky radar images? :)

Their reply was an eye opener. They said there are two schools of thoughts and that they have debates all the time on this topic. On school of thought is to display the radar image *exactly* as it was received from the source. In this regards you will see a blocky image. This is what IFlygps does. What you see is what you get.

The other school of thought is to interpret and extrapolate the data to create a smooth image that looks different from what was received from the source. What you see is slightly different from what was received To your point FF is passing the data received through their algorithm then rendering.
 
I think that I found some charts that explain this. Under the standard NOAA protocol, 35 is dark green and 40 is yellow. The GRT format is yellow from 30-40 and the FF format is green from 30-40. I guess one is a bit conservative and the other a bit liberal. Suppose that I will learn to split the difference between them.

Larry
 
drill_and_buck said:
Interesting observation..

This doesn't answer your question but here is another data point to consider. At KOSH I was speaking to the IFlygps folks about how they render their radar images. I was curious in this day and age why some of the images you see on EFB Apps are pixelated while others have smooth boundaries. In brief I was asking him why they are painting blocky radar images? :)

Their reply was an eye opener. They said there are two schools of thoughts and that they have debates all the time on this topic. On school of thought is to display the radar image *exactly* as it was received from the source. In this regards you will see a blocky image. This is what IFlygps does. What you see is what you get.

The other school of thought is to interpret and extrapolate the data to create a smooth image that looks different from what was received from the source. What you see is slightly different from what was received To your point FF is passing the data received through their algorithm then rendering.
Click to expand...

I would think the former is probably better. The transmitted blocks are certainly averaged / interpolated representations of the original radar image, so smoothing and interpreting again may not be best, though looks more appealing.

Larry
 
Mark Dickens said:
There is a setting in FF which allows you to choose between 4 color radar and 5 color...as to how to match it up with nexrad, I don't know. Looks like there's some good info here: https://blog.foreflight.com/tag/weather. Look about 2/3s the way down on that page.
Click to expand...

Thanks for that link. It looks like GRT is using that RTCC convention (4 color) for their coloring. It's interesting that the one format puts yellow at 30-40 and the other from 40-45. It seems this RTCC is closer to the XM format as well. Unfortunately, they both straddle the NOAA yellow = 35. I think that I'll keep the current setting, as then I'll see two different interpretations of the weather and use judgement to decide how bad it is.
 
I have noticed that Garmin Pilot also shows the same radar picture with "scarier" (heavier precip) Nexrad colors than other (non-aviation) tools. I always assumed they were being more conservative due to liability concerns.
 
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