GPS/XM Weather Question

"Ron Natalie" wrote in message
m...
There aren't operators intervening most likely, but the data is far from
a simple "photographic image." The thing is intensity adjusted, noised
filtered, and geometrically remapped before it comes out in the format
that you see it in weathermation or whatever.

I understand that there is image processing to make it suitable for
presentation in a given format. But that doesn't mean that there's someone
dropping clouds from the picture when they are there originally.

".Blueskies." wrote in message
t...
All said and done, I still consider the monthly ~$30 charge to be a user
fee of sorts. You can call FSS on the radio or
pay the fee and receive the same info. More convenient to use the GPS?
Maybe for some...

Well, I don't do enough cross-country flying these days to justify the cost,
but certainly back when I did, I would have loved the convenience and
probably would've found $30 to be reasonable. It can sometimes be a hassle
just getting the FSS to reply on either Flight Watch or an RCO, depending on
how busy they are, and even once you do, you are basically relying on them
to be able to describe in words the situation.

For some things, like METARs and TAFs, the language barrier isn't a problem,
but when dealing with graphical depictions of things like rain, lightning,
or even clouds (as non-useful as I think the cloud picture is most of the
time ), there's no substitute for a good picture. To be able to present
the picture in real-time relative to your course (planned or current) is
even better, and something you just can't get using the FSS directly.

I guess it depends on your definition of "user fee", but I don't see it that
way. First, the fee isn't being paid to the government...it's being paid to
a commercial service offering something that the government doesn't provide,
even if the underlying data is from the government. Second, we pay the
government for a variety of other services now, mostly related to charting.
I've never heard anyone complain about "user fees" when buying sectionals,
A/FDs, WACs, IFR charts or approach plates, nor have I ever heard anyone
describe Jeppesen's product as being paid for with "user fees".

Pete

"Bob Noel" wrote in message
...
IIRC visible satellite images will show low clouds as very dark... the
bright
clouds are higher. Are you sure it showed no cloud-cover?

Visible satellite should not vary in brightness according to altitude. But
infrared does. Perhaps the XM images are from the infrared satellite, as
Casey suggests.

In article .com,
"Jay Honeck" wrote:
Obviously, in changing flight conditions this slow rate of change is
simply unacceptable, and we quickly reverted to listening to AWOS's
ahead on the radio.

Strike two for XM.

I suspect that the METAR data was being updated as expected, but the
METARs don't change but once an hour, unless there's a SPECI issued.
Same data as is available from flight service or DUATS.



JKG

In article ,
".Blueskies." wrote:
: As I already said, all that XM does for you is show you the data in a
: friendlier way, and avoid the radio call to the FSS. Expecting more from
: them is unreasonable and will guarantee disappointment on your part.
:
: Pete
:
:

All said and done, I still consider the monthly ~$30 charge to be a user fee
of sorts. You can call FSS on the radio or
pay the fee and receive the same info. More convenient to use the GPS? Maybe
for some...

It isn't the same information. There is no substitute for having all
data front of you, and not having to waste time trying to figure out
what you're about to fly into, praying that someone will answer you on
Flight Watch, and then having to rely on that person's interpretation of
the weather. There's just no comparison whatsoever.

And your notion of the XM subscription cost being a "user fee" is
ridiculous, as I've pointed out previously.



JKG

In article ,
"Peter Duniho" wrote:


Visible satellite should not vary in brightness according to altitude. But
infrared does. Perhaps the XM images are from the infrared satellite, as
Casey suggests.

hmmm. Looking at sat pictures from http://adds.aviationweather.gov/satellite/,
the visible sat picture sure seems like the brightness varies with altitude,
if only because the higher clouds can catch more sunlight.

But the B&W infrared images don't seem as good at showing low clouds
as the visible sat images.

The color infrared and the water vapor images are definitely better
at showing lower clouds.

--
Bob Noel
Looking for a sig the
lawyers will hate

What is Atlas' tail number again? I might be coming your way next month.

No need for it, but here it is:

We'll look forward to your (potential) visit!

:-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Sounds a little bit like you were expecting the 496 to be a panacea for
all things weather and it turns out to be just a system of displaying
information you could get from other sources.

This is true to some degree. I had hoped that the airport information
from AWOS's and ASOS's would update at the same rate as the NEXRAD
(every 6 - 10 minutes), rather than just once per hour -- but I never
really inquired about this, so I have only myself to blame.

The main purpose for purchasing the unit -- weather avoidance and
awareness -- is still 100% valid when it comes to precip and convective
activity. I'm just not going to be able to use XM to avoid skanky
visibilities or ceilings, as I had hoped.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

"Bob Noel" wrote in message
news:ihatessppaamm-
hmmm. Looking at sat pictures from
http://adds.aviationweather.gov/satellite/,
the visible sat picture sure seems like the brightness varies with
altitude,
if only because the higher clouds can catch more sunlight.

But the B&W infrared images don't seem as good at showing low clouds
as the visible sat images.

The color infrared and the water vapor images are definitely better
at showing lower clouds.

--
Bob Noel
Looking for a sig the
lawyers will hate

Hmmmm, first, you are not going to see any clouds or water vapor with
the infrared -- they are transparent to the photon energy being emitted by
the stuff below.
Second, any color other than a shade of grey in an infrared image is a
false color assigned to a discrete slice of the grey range. While the true
grey range may be 2**8, the false color range will (usually) only be 2**3.
The only reason to use false color is that the eye discerns adjacent 2**3
colors easier than 2**8 shades of grey.
Which brings up a third point. When you see varying color overlays --
like red for the center of a cell, then expanding out to orange, yellow and
eventually green -- it is unlikely they are infrared images. The infrared
image is derived by apparent differences in temperature. In a typical
rainstorm, the temperatures are close to equilibrium.

It is time now for me to waffle a bit. Sure as the sun came up this
morning, somebody will find a paper contradicting me. So, I confess, clouds
and water vapor are not 100% transparent to LWIR. But (there's always a big
butt), the emissivity is so low, it can't be detected with the relatively
crude instruments in the satellites as compared to a high-resolution, FFT
based, infrared spectrometer in a laboratory.

I figured you wuld be a good person to ask, so here goes.

I'm heading to Washington, (by car) and am going to be staying at a Regan
airport hotel.

What is the best way to get from there to Udvar-Hazy Annex? Is there a
shuttle, or train, or something?
--
Jim in NC