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Archive for the ‘Passive Microwave’ Category

SPoRT continues to work with select NWS WFOs in evaluating the NESDIS SFR product.

One thing to take into consideration when using data from “whisk-broom” instruments on polar-orbiting satellites, such as the Advanced Microwave Sounding Unit (AMSU) used to generate the SFR product, is that data at the edge of the swath (i.e. limb) may provide misleading or erroneous observations. As the instrument scans farther from nadir, it is looking through more of the atmosphere, creating both a bigger observation field of view (i.e., larger pixel) and having the signal attenuated by more atmospheric constituents (e.g., in-cloud and falling snow).  As a result, when interpreting the SFR product, it is important to look for the extent of the swath (outlined in gray in the product in AWIPS) to determine whether the observed SFR is going to be limited by these limb effects.

Let’s take a look at an example over the NY Tri-State area for the post Super Bowl snow event.  In the first image, from Metop-A valid at 1458 UTC, there is a large area of snowfall across the area.  The heaviest SFRs appear to be around 1.2-1.5 in/hr (when multiplying the liquid equivalent by 10) across central and southern New Jersey.  However, an hour later (see second image from Metop-B valid at 1554 UTC), the shape of the heaviest SFR has expanded north and west and there are now readings over 2.0 +in/hr.  Other areas that had a SFR of less than 0.5 in/hr in the 1458 UTC image, appear to have a SFR of around 1.0 in/hr just an hour later, which is a large jump in intensity.

While it is certainly possible that the snow evolved and intensified in less than an hour, it is more likely that instrument limb effects are likely to blame for the larger SFRs in the second image.  Make sure to check that swath edge when using polar-orbiting satellite data!

NESDIS SFR Product from 1458 UTC on 3 February 2014 showing snow detected near nadir for Metop-A

NESDIS SFR Product from 1458 UTC on 3 February 2014 showing snow detected near nadir for Metop-A.

NESDIS SFR Product from 1554 UTC on 3 February 2014 depicting what are likely erroneous higher intensity SFR values along the swath edge from Metop-B.

NESDIS SFR Product from 1554 UTC on 3 February 2014 depicting what are likely erroneous higher intensity SFR values along the swath edge from Metop-B.

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SPoRT continues to work with select NWS WFOs in evaluating the NESDIS SFR product.

A rare winter storm impacted much of the deep South Tuesday morning and afternoon.  Areas of Central and Northeastern Alabama only received a couple of inches of snow, but this was enough to cause major headaches as roadways iced over resulting in highways across Alabama and Georgia being shut down, stranding thousands of motorists.  Most reports from late Tuesday morning indicated that the worse of the winter weather was falling south of Cullman, AL, through Birmingham, AL to Montgomery, AL and then eastward into areas like Fort Payne, AL.  I-65 north of Birmingham and I-20 east of Birmingham were particularly troublesome in the state of Alabama.

The AWIPS image below depicts the SFR product in AWIPS with overlaid interstate highways.  This image was taken from the AMSU on Metop-B at 1618 UTC (10:18 local Alabama time) right about the time when the heaviest snow was impacting the state.  The SFR Product indicates liquid water equivalent precipitation rates between 0.04 and 0.08 in/hr, which if you multiply by a factor of 10 to get the solid snowfall rate equates to around 0.4 and 0.8 in/hr.  Snowfall totals across this region were generally in the 1-3 inch range, so the rates that were detected by the product were consistent with what actually fell.

NESDIS SFR Product from 1618 UTC (around 10:00 A.M. Central) on 28 January 2014

NESDIS SFR Product from 1618 UTC (around 10:00 A.M. Central) on 28 January 2014

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SFR_1605UTC_012614

On Jan 26 2014, an upper level shortwave caused an area of light snow across Ohio, western Pennsylvania and the northern counties of West Virginia. Surface temperatures were quite cold with readings generally in the teens. Even at these cold temperatures, the SFR product did indicate snowfall across the far northern counties of our forecast area.

The maximum snowfall rates indicated on the 1605 UTC product was about 0.3 to 0.4 inches per hour. Based on reports, these numbers appear to be representative of what actually was occurring.

While this is just one case, the SFR product appears to work reasonably well at temperatures below 22 DegF.

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Radar_1106UTC_012514SFR_1120UTC_012514

On Jan 25 2014, a mid-level shortwave moved across the region generating light to moderate snow. I have included screen captures of the 1118 UTC regional radar mosaic and surface observations…along with a 1120 UTC Snowfall Rate Product and surface observations.

It looks like the SFR product did not detect all of the snow that was falling around 11 UTC. But the misses can generally be described as either (1) the surface temperatures being too cold or (2) the probabilistic model, that is part of the calulations, indicating probabilities that were too low to determine if there was snow.

Once you know all of the details on how the product is calculated, I think this product did a good job at detailing where the snowfall was occurring.

The highest snowfall rates indicated by this image was around 0.3 to 0.5 inches which seems to be representative of what was occurring.

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SFR_1522UTC_012114

When I examined the 1522 UTC SFR product, I noticed there was an absence of snow across our forecast area. Radar and surface observations indicated that light to moderate snow was continuing across most of our counties.

Per the Quick Guide, I checked the surface observations to see if the temperatures were about 22 DegF or colder. The temperatures across our northern and western counties were actually 22 DegF or colder. So the SFR product was behaving as it should across those counties.

However, the temperatures across the remainder of our region were above 22 DegF. The snow is definitely not lake effect as the current snow was still related to a shortwave which had pushed to our east.

What could be causing the lack of indicated snow across the portions of our area that still had surface temnperatures above 22 DegF?

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All,

I have attached a screen capture of the SFR product from 1024 UTC on 1/21/14.  The label on the image is wrong.  It states the units of the product are in/hr.  But they are actually mm/hr.

During this time, we were having widespread light to moderate snow as an upper level disturbance moved across our forecast area.  Reports around 2 inches of snow were common around the time of the product.   We had received reports of snow coming down around an inch per hour.  The maximum SFR detected in the product was 1.6 mm/hr…or 0.06 in/hr.  Using a ratio of 15:1 yields a maximum snowfall rate around 0.9 inches per hour.

While we had several surface observations from which we could estimate precipitation rates, our WSR-88D was not operating correctly.  The legacy precipitation were okay.  But the Dual Pol precipitation products were not totally reliable due to equipment issues.  So the additional information from the SFR product should have helped estimate the precipitation rates.

SFR_1024Z_012114

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Moisture plumes from the tropical Pacific can extend into the mid-latitudes, and the CIRA Layer Precipitable Water (LPW) product based on microwave (AMSU, MHS) and infrared (AIRS) sounding instruments from NASA and NOAA polar-orbiting satelliltes provides information on the amount of moisture in each layer.  Traditional total precipitable water (TPW) data only give part of the picture and Water Vapor (WV) imagery only captures the upper tropospheric moisture.  Note here how the GOES WV imagery from the NASA GHCC site agrees well with the values of 2-4 mm in the 500-300 mb layer between Hawaii and the west CONUS.

20130313_2100_sport_cira_west_lpw500to300hpa

500-300 mb Layer Precipitable Water by CIRA, 13 March 2013, 2100Z

20130313_2130_GHCC_GOESW_WV

GOES Water Vapor imagery from NASA GHCC site, 13 March 2013, 2130Z

In the images below, the surface to 850 mb layer shows a wide plume of 0.5 to 0.75 inches of PW extending from Hawaii to Washington and Oregon. Moving upwards, the 850 to 700 mb layer continues to show a wide swath of moisture (~0.25 to 0.5 inches) in this same area, with a sharp gradient to the east.  Lastly, the 700 to 500 mb layer shows a more narrow moisture swath, but still with values ranging from ~0.25 to 0.33 inches, and extending into the northwest CONUS. The observations of vertical distribution of moisture in data void regions can be compared to NWP models as well as applied to estimating the available moisture at low levels for potential precipitation and flooding events.

20130313_2100_sport_cira_west_lpwsfcto850hpa

Surface to 850 mb Layer Precipitable Water by CIRA, 13 March 2013, 2100Z

20130313_2100_sport_cira_west_lpw850to700hpa

850 to 700 mb Layer Precipitable Water by CIRA, 13 March 2013, 2100Z

20130313_2100_sport_cira_west_lpw700to500hpa

700 to 500 mb Layer Precipitable Water by CIRA, 13 March 2013, 2100Z

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SPoRT’s Disaster Response Team sprung into action this morning to produce imagery in response to Super Typhoon Bopha as it approaches The Philippines and the Southeast Asia mainland.  To better serve SPoRT’s partners, end-users, and the general public, this imagery has been integrated into SPoRT’s new Tiled Mapping Service (TMS).  The TMS allows users the capability to view the highest resolution data using only their web browser.  This service is also helpful for disaster response teams that are working in the field as browsers on tablets or smartphones can seamlessly pan and zoom SPoRT imagery without the need for a specific decision support system, lots of computational horsepower, or fast data download speeds.  In addition, users can adjust the transparency of different data sets in order to compare features from multiple instruments.  The transparency can be adjusted by clicking on the text associated with the displayed product in the layer tree and then using the scroll bar in the upper left of the display to adjust the transparency.

Below is an example of using the TMS to layer Day Night Band (DNB) imagery from NASA/NOAA/DoD’s Visibile Infrared Imaging Radiometer Suite (VIIRS) valid at around 1700 UTC on 2 December 2012 and the 89 GHz RGB product from NASA’s Tropical Rainfall Measurement Mission (TRMM) Microwave Imager.  In the VIIRS image, cloudy features appear as white even in the middle of the night as moonlight is reflected from the cloud tops.  Here, Super Typhoon Bopha can be seen in the bottom right of the VIIRS swath.  However, the edge of the scan bisects the storm.  To get a more full picture of the storm–and to learn additional information about where active convection is occurring–the passive microwave 89 GHz RGB product can be overlain.  With the transparencies appropriately adjusted, one can see both the extent of the cloud field associated with the storm (white features in the VIIRS DNB imagery) along with areas that are most convectively-active (red areas in PM RGB).

SPoRT continues to process additional datasets to add into the system, so check back for updates as new satellite data become available.

Example of overlaying NASA satellite datasets in SPoRT's TMS.  Passive Microwave RGB imagery from 0200 UTC on 3 December overlays VIIRS DNB  imagery from 1700 UTC on 2 December for Super Typhoon Bopha as it approaches The Phillipines

Example of overlaying NASA satellite datasets in SPoRT’s TMS. Passive Microwave RGB imagery from TRMM is overlaid on VIIRS DNB imagery to show where most active convection is occurring with Super Typhoon Bopha as it approaches The Philippines.

High-resolution VIIRS DNB Imagery of Super Typhoon Bopha from SPoRT TMS displayed using a handheld device.

High-resolution VIIRS DNB Imagery of Super Typhoon Bopha from SPoRT TMS displayed using a handheld device.

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Following up from our previous post regarding Aletta, today’s pass of DMSP F-18 (1535 UTC) was nicely centered over Tropical Storm Bud, located southwest of Mexico in the eastern Pacific.  The 1500 UTC advisory suggests maximum sustained winds of 65 mph and northwest motion, with a northern turn expected.  It may progress to develop into a hurricane later today or tonight.  Below are current snapshots of RGB passive microwave composites provided to SPoRT via collaboration with the Naval Research Laboratory, converted to use in GEMPAK and N-AWIPS.  The 89 GHz image (top) includes estimates of the observation time (1530-1535 UTC) and the satellite instrument (DMSP F-18).  These composites demonstrate how passive microwave data can help to identify structures of the tropical cyclone that might otherwise be obscured by thick cirrus overhead.  SPoRT plans to collaborate with NCEP groups to test and evaluate these products in N-AWIPS in support of our NRL collaboration, as these products have been very popular when provided by the NRL Tropical Cyclones web page.

91 GHz RGB composite image from DMSP F-18 SSMI/S sensor over Tropical Storm Bud at approximately 1530 UTC on May 23, 2012.

As in the image above but for the 37 GHz channels.

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Tropical Depression Aletta is slowly churning through the eastern Pacific, currently located southwest of Baja California in the Eastern Pacific.  As of 0800 PDT, the latest forecast advisory estimates peak winds of 35 mph and the storm is expected to weaken.  However, the presence of the storm is a great opportunity to feature the results of a collaboration between the Naval Research Laboratory and the SPoRT Center that has facilitated the integration of NRL passive microwave products into the N-AWIPS visualization system (which is based upon GEMPAK capabilities).  Below are some comparisons between graphics provided by the NRL Tropical Cyclones page.  SPoRT has developed display capabilities for NRL single channel and multispectral (RGB) passive microwave products along with an estimate of the observing time based upon the satellite orbit.  These images were obtained from the DMSP F-17, although data from the full constellation of DMSP satellites and NASA’s Tropical Rainfall Measuring Mission (TRMM) are also available.  Since these satellites have slightly different orbits, each snapshot of the storm is provided to SPoRT by NRL, and data are processed for display in N-AWIPS and distributed to partnering NCEP locations.

Low frequency (37 GHz) passive microwave RGB composite of Aletta at approximately 1305 UTC, based upon observations form DMSP F-17.

Equivalent to image above, produced by SPoRT from NRL data and configured for display in N-AWIPS (GEMPAK) for dissemination to partnering NCEP Centers.

High frequency (87-91 GHz) image of Aletta provided by the NRL Tropical Cyclones page.

Equivalent image processed by SPoRT for dissemination in N-AWIPS.

 

Although the zoom factor is slightly different between the NRL image and the N-AWIPS examples, the display of the data in N-AWIPS will allow forecasters to have greater control in manipulating the imagery and collocating satellite observations with other analyses available within their local systems.

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