GDL-49 and Levels of Radar Returns

As I was coming into Grand Rapids (KGRR) yesterday, the controller
announced that there was a "level 5" return (or perhaps she said "cell")
on final to runway 8, so I was vectored to 35 where there were mostly
"just level 4" stuff. So, forgive my ignorance, but where are these
levels defined? I assume they have to do with what sort of radar return
they get off a cloud and therefore has to do with rain intensity. Does
a level 5 return imply that a thunderstorm is likely to be generating it?

Also, I have a GDL-49 Satellite Data Link Transceiver linked to my
Garmin 430 display. I understand (and now have seen) that these things
just are not adequate to locate big cells. Rather, they show large
areas of showers. Are these based on satellite imagery, or from
aggregated ground station data or what?

Also, how to the radar levels (1 thru 6?) relate to the colors shown on
a GDL-49 display on a Garmin 430? Does red equal level 5 or level 6? I
think only have red, yellow and green...so it seems there are not
enough colors to show 6 levels.

-Sami, N2057M, Piper Turbo Arrow III

"O. Sami Saydjari" wrote:

As I was coming into Grand Rapids (KGRR) yesterday, the controller
announced that there was a "level 5" return (or perhaps she said "cell")
on final to runway 8, so I was vectored to 35 where there were mostly
"just level 4" stuff. So, forgive my ignorance, but where are these
levels defined? I assume they have to do with what sort of radar return
they get off a cloud and therefore has to do with rain intensity. Does
a level 5 return imply that a thunderstorm is likely to be generating it?

Also, I have a GDL-49 Satellite Data Link Transceiver linked to my
Garmin 430 display. I understand (and now have seen) that these things
just are not adequate to locate big cells. Rather, they show large
areas of showers. Are these based on satellite imagery, or from
aggregated ground station data or what?

Also, how to the radar levels (1 thru 6?) relate to the colors shown on
a GDL-49 display on a Garmin 430? Does red equal level 5 or level 6? I
think only have red, yellow and green...so it seems there are not
enough colors to show 6 levels.

-Sami, N2057M, Piper Turbo Arrow III

You might try checking the AIM, for starters. Then, perhaps, the IHB.

Tim,

Chapter 1, section 1 of the AIM would seem to be most appropriate for
this question, and I have found no references to radar echoes. If you
have a pointer to the information that you think answers my question,
that would be helpful.

Please forgive my ignorance, but I do not know the acronym "IHB."
Please expand.

I have also tried Circular AC-00-6A, and did not find it.

I would also note that note of these sources is likley to answer the
questions of color mapping on a GDL-49/Garmin 430.

-Sami

wrote:


"O. Sami Saydjari" wrote:


As I was coming into Grand Rapids (KGRR) yesterday, the controller
announced that there was a "level 5" return (or perhaps she said "cell")
on final to runway 8, so I was vectored to 35 where there were mostly
"just level 4" stuff. So, forgive my ignorance, but where are these
levels defined? I assume they have to do with what sort of radar return
they get off a cloud and therefore has to do with rain intensity. Does
a level 5 return imply that a thunderstorm is likely to be generating it?

Also, I have a GDL-49 Satellite Data Link Transceiver linked to my
Garmin 430 display. I understand (and now have seen) that these things
just are not adequate to locate big cells. Rather, they show large
areas of showers. Are these based on satellite imagery, or from
aggregated ground station data or what?

Also, how to the radar levels (1 thru 6?) relate to the colors shown on
a GDL-49 display on a Garmin 430? Does red equal level 5 or level 6? I
think only have red, yellow and green...so it seems there are not
enough colors to show 6 levels.

-Sami, N2057M, Piper Turbo Arrow III


You might try checking the AIM, for starters. Then, perhaps, the IHB.

Rod Machado's column in the latest AOPA Pilot covers the subject very well.

Gerry

"O. Sami Saydjari" wrote in message
...
As I was coming into Grand Rapids (KGRR) yesterday, the controller
announced that there was a "level 5" return (or perhaps she said "cell")
on final to runway 8, so I was vectored to 35 where there were mostly
"just level 4" stuff. So, forgive my ignorance, but where are these
levels defined? I assume they have to do with what sort of radar return
they get off a cloud and therefore has to do with rain intensity. Does a
level 5 return imply that a thunderstorm is likely to be generating it?

Also, I have a GDL-49 Satellite Data Link Transceiver linked to my Garmin
430 display. I understand (and now have seen) that these things just are
not adequate to locate big cells. Rather, they show large areas of
showers. Are these based on satellite imagery, or from aggregated ground
station data or what?

Also, how to the radar levels (1 thru 6?) relate to the colors shown on a
GDL-49 display on a Garmin 430? Does red equal level 5 or level 6? I
think only have red, yellow and green...so it seems there are not enough
colors to show 6 levels.

-Sami, N2057M, Piper Turbo Arrow III

In googling around a bit, I found the following:

------------------------------------------------------------------------

At: http://www.weatherzone.com.au/misc/g...y.jsp?letter=V

"Video Integrator and Processor, which contours radar reflectivity (in
dBZ) into six VIP levels:
• VIP 1 (Level 1, 18-30 dBZ) - Light precipitation
• VIP 2 (Level 2, 30-38 dBZ) - Light to moderate rain.
• VIP 3 (Level 3, 38-44 dBZ) - Moderate to heavy rain.
• VIP 4 (Level 4, 44-50 dBZ) - Heavy rain
• VIP 5 (Level 5, 50-57 dBZ) - Very heavy rain; hail possible.
• VIP 6 (Level 6, 57 dBZ) - Very heavy rain and hail; large hail possible."

---------------------------------------------------------------------------
At:
http://www.garmin.com/manuals/773_Ga...deAddendum.pdf

Ok, now, from the Nextrad intensity table on page 13 of the Garmin
"400/500 Series garmin Options Displays", I learned:

GREEN means 5-30 dBZ
YELLOW means 30-55 dBZ
RED means 55-75 dBZ

So...
Green is VIP Level 1
Yellow is VIP Levels 2,3,4
Red is VIP levels 5 and 6

The radar appears to come from an aggregation of ground NEXTRAD sites,
that is beamed up via satellite based on user request messages.



O. Sami Saydjari wrote:

As I was coming into Grand Rapids (KGRR) yesterday, the controller
announced that there was a "level 5" return (or perhaps she said "cell")
on final to runway 8, so I was vectored to 35 where there were mostly
"just level 4" stuff. So, forgive my ignorance, but where are these
levels defined? I assume they have to do with what sort of radar return
they get off a cloud and therefore has to do with rain intensity. Does
a level 5 return imply that a thunderstorm is likely to be generating it?

Also, I have a GDL-49 Satellite Data Link Transceiver linked to my
Garmin 430 display. I understand (and now have seen) that these things
just are not adequate to locate big cells. Rather, they show large
areas of showers. Are these based on satellite imagery, or from
aggregated ground station data or what?

Also, how to the radar levels (1 thru 6?) relate to the colors shown on
a GDL-49 display on a Garmin 430? Does red equal level 5 or level 6? I
think only have red, yellow and green...so it seems there are not
enough colors to show 6 levels.

-Sami, N2057M, Piper Turbo Arrow III

"O. Sami Saydjari" wrote in message ...
As I was coming into Grand Rapids (KGRR) yesterday, the controller announced that there was a "level 5"
return (or perhaps she said "cell") on final to runway 8, so I was vectored to 35 where there were mostly
"just level 4" stuff. So, forgive my ignorance, but where are these levels defined? I assume they have to
do with what sort of radar return they get off a cloud and therefore has to do with rain intensity. Does a
level 5 return imply that a thunderstorm is likely to be generating it?


By the way, when you flew through the "just level 4 stuff", how did you find the ride?

--
Cheers,
John Clonts
Temple, Texas
N7NZ

Surprisingly, the most I experienced was light turbulence. The landing
was uneventful. At the same time, I expect I was pretty lucky and
probably will actively avoid landing in these sorts of conditions in the
future.

My NEXTRAD showed "green" so I was unconcerned going in. It was only
from approach that I started hearing about level 4 and leve 5 stuff
around the airport. Had I known, I would have diverted north.

-Sami
N2057M, Piper Turbo Arrow III


John Clonts wrote:
"O. Sami Saydjari" wrote in message ...

As I was coming into Grand Rapids (KGRR) yesterday, the controller announced that there was a "level 5"
return (or perhaps she said "cell") on final to runway 8, so I was vectored to 35 where there were mostly
"just level 4" stuff. So, forgive my ignorance, but where are these levels defined? I assume they have to
do with what sort of radar return they get off a cloud and therefore has to do with rain intensity. Does a
level 5 return imply that a thunderstorm is likely to be generating it?



By the way, when you flew through the "just level 4 stuff", how did you find the ride?

O. Sami Saydjari wrote:

As I was coming into Grand Rapids (KGRR) yesterday, the controller
announced that there was a "level 5" return (or perhaps she said "cell")
on final to runway 8, so I was vectored to 35 where there were mostly
"just level 4" stuff.

That's pretty funny because even the airlines ain't flying thru a level
four return on final.

Sami, you've hit upon the answer to your question, and one thing to keep in
mind is that radar don't know squat about whether the rain is from a
thunderstorm or not, all it sees is the "reflection" of the precip, the
higher the number, the higher the bounce back. Granted, a thunderstorm that
is full of rain and hail will definately produce a higher return.
Additional information about the current conditions vs. forecast conditions
combined with front locations, movement, direction, sigmets, and airmets
should provide you with a more complete picture of what your Data Link is
showing you.

Over the past couple weeks, we've had two totally different low pressure
systems move through Wisconsin. The first contained a leading edge of
thunderstorms, high winds and heavy rain. The last contained high winds,
heavy rain, but no thunderstorms. The echoes for both storms were level 2's
and 3's. The difference between the two storms was the amount of lifting
action available. The first storm occurred during a period of relatively
hot and unstable conditions. The second occurred during cool and more
stable conditions, it was much less violent but the radar returns were the
same.

Jim Burns


"O. Sami Saydjari" wrote in message
...
In googling around a bit, I found the following:

------------------------------------------------------------------------

At: http://www.weatherzone.com.au/misc/g...y.jsp?letter=V

"Video Integrator and Processor, which contours radar reflectivity (in
dBZ) into six VIP levels:
• VIP 1 (Level 1, 18-30 dBZ) - Light precipitation
• VIP 2 (Level 2, 30-38 dBZ) - Light to moderate rain.
• VIP 3 (Level 3, 38-44 dBZ) - Moderate to heavy rain.
• VIP 4 (Level 4, 44-50 dBZ) - Heavy rain
• VIP 5 (Level 5, 50-57 dBZ) - Very heavy rain; hail possible.
• VIP 6 (Level 6, 57 dBZ) - Very heavy rain and hail; large hail
possible."

--------------------------------------------------------------------------
-
At:

http://www.garmin.com/manuals/773_Ga...deAddendum.pdf

Ok, now, from the Nextrad intensity table on page 13 of the Garmin
"400/500 Series garmin Options Displays", I learned:

GREEN means 5-30 dBZ
YELLOW means 30-55 dBZ
RED means 55-75 dBZ

So...
Green is VIP Level 1
Yellow is VIP Levels 2,3,4
Red is VIP levels 5 and 6

The radar appears to come from an aggregation of ground NEXTRAD sites,
that is beamed up via satellite based on user request messages.



O. Sami Saydjari wrote:

As I was coming into Grand Rapids (KGRR) yesterday, the controller
announced that there was a "level 5" return (or perhaps she said "cell")
on final to runway 8, so I was vectored to 35 where there were mostly
"just level 4" stuff. So, forgive my ignorance, but where are these
levels defined? I assume they have to do with what sort of radar return
they get off a cloud and therefore has to do with rain intensity. Does
a level 5 return imply that a thunderstorm is likely to be generating
it?

Also, I have a GDL-49 Satellite Data Link Transceiver linked to my
Garmin 430 display. I understand (and now have seen) that these things
just are not adequate to locate big cells. Rather, they show large
areas of showers. Are these based on satellite imagery, or from
aggregated ground station data or what?

Also, how to the radar levels (1 thru 6?) relate to the colors shown on
a GDL-49 display on a Garmin 430? Does red equal level 5 or level 6? I
think only have red, yellow and green...so it seems there are not
enough colors to show 6 levels.

-Sami, N2057M, Piper Turbo Arrow III

Newps wrote:



O. Sami Saydjari wrote:

As I was coming into Grand Rapids (KGRR) yesterday, the controller
announced that there was a "level 5" return (or perhaps she said
"cell") on final to runway 8, so I was vectored to 35 where there were
mostly "just level 4" stuff.


That's pretty funny because even the airlines ain't flying thru a level
four return on final.


That is pretty odd. I am sure she said level 4. The rain seemed only
moderate to me and visibility seemed like it was 2-3 miles. Perhaps I
got lucky. How sure are you that airlines do not land in level 4? If
so, it seems that they would advise a light aircraft to divert or hold.