Weather Radar Question?

[AdamZ]

In using the ADDs pages on NOAAs Aviation weather site I often check the Radar Images. What is the difference between Composite Reflectivity and Base Reflectivity?

 

[Steve]

http://www.srh.noaa.gov/radar/radinfo/radinfo.html#base

Base reflectivity only shows reflected energy at a single elevation scan of the radar. Composite reflectivity displays the highest reflectivity of ALL elevations scans.

 

[Joe B]

Steve got it right. It's worth noting that some in the aviation press think that "base reflectivity" is only the bottom scan or, somehow, what's going on at the cloud bases. These interpretations are incorrect. Base reflectivity is the data from one single scan at any elevation.

Regards,
Joe

 

[Dave Siciliano]

Adam:

That's why those of us with on-board have an advantage; between scan and tilt, we can focus on different altitudes. Base or composite give a good general idea; on-board slices and dices (like the old Ronco products ;-)).

Best,

Dave

 

[MauleSkinner]

I was able to show my boss the difference really well one day...we were watching my Dad fly the Baron on the flight tracker, and he was heading way off-course. Boss was wondering why, because the radar didn't look that bad...I switched it to "composite", and he understood

Fly safe!

David

 

[AdamZ]

Hey guys thanks for the info. Steve thanks so much for the link. Aviaiton weather is something I am prepetually trying to get a better understanding of. As Dave said Composite slices and dices like the old Ronco. I was thinking of and MRI of the weather system but same Idea.

Does base reflectivity state the altitude it is taking the slice from and dose NOAA lilke to take a particular slice AGL when putting out a base chart?

 

[Steve]

I think you have to interpolate the height of the reflected image using the distance and angle from the radar site...I've never had much success finding real time info for cloud tops beyond the rare pilot report. I often see the terms "cloud height" and "cloud top" interchanged, too. Remember, too, that the radar data display is geared toward surface activities, not airborne ones. Having an onboard radar certainly improves the accuracy of the imaging for aeronautical use.

The only reason I knew the site had the info was I book marked it after looking for the same answer a while back.

From the same link:

In clear air mode, the radar begins a volume scan at the 0.5° elevation angle (i.e., the radar antenna is angled 0.5° above the ground). Once it makes two full sweeps (a surveillance/reflectivity sweep and a Doppler/velocity sweep) at the 0.5° elevation angle, it increases to 1.5° and makes two more 360° rotations. For one of the clear air mode VCPs (volume coverage pattern), two full sweeps are also made at 2.5°. Otherwise, at the higher elevations (2.5°, 3.5°, and 4.5°) a single sweep is made (reflectivity and velocity data are collected together).

This process is repeated at 2.5°, 3.5°, and 4.5°. Then the radar returns to the 0.5° elevation angle to begin the next volume scan which will repeat the same sequence of elevation angles. In clear air mode, the complete scan of the atmosphere takes about 10 minutes at 5 different elevation angles.

The base reflectivity image currently available on this website is from the lowest "tilt" angle (0.5°). This means the radar's antenna is tilted 0.5° above the horizon.

Precipitation Mode

The difference is the radar continues looking higher in the atmosphere, up to 19.5° to complete the volume scan. The time it takes to complete the entire volume scan is also less. In the slower VCP, the radar completes the volume scan of nine different elevations in six minutes. In the faster VCP, the radar completes 14 different elevation scans in five minutes.

A little more digging and I found more technical data on NEXRAD operation available at:

http://www.roc.noaa.gov/FMH_11/default.asp

Hey guys thanks for the info. Steve thanks so much for the link. Aviaiton weather is something I am prepetually trying to get a better understanding of. As Dave said Composite slices and dices like the old Ronco. I was thinking of and MRI of the weather system but same Idea.

Does base reflectivity state the altitude it is taking the slice from and dose NOAA lilke to take a particular slice AGL when putting out a base chart?