Checking Sight Reduction With CelestialTools.exe

CelestialTools.exe is a free PC program that solves many problems in cel nav and other areas. It was written by the late Stan Klein, navigator, teacher, and friend. It was written for USPS students and instructors, but Stan decided to share it with the public several years ago and ask us to host it, which we were happy to do.  It is a wonderful tool for learning cel nav, especially with regard to one unique function it includes called "SR Methods and Fix." Download celestial tools and its manual.

Below is the graphic menu to the program (Windows only). The function at hand now is far left of the middle row.

Figure 1 Splash screen index.  (Click any image for a better view.)

Here is the motivation for this note. A student working a sight reduction using the NAO Sight Reduction tables got the wrong answer, and submitted this form for us to check. This is one of the Starpath work forms, available online as blank forms. The instructions and examples are in a separate book.

We are happy to make such checks for our students, but we try to encourage them to use CelestialTools as it is a way to find mistakes much faster than waiting for our response. This note here is just a reminder about how this works. You can use it to check any type of sight reduction.

Figure 2. An NAO form with wrong data.

This has the wrong answer. Recall that a sight reduction means we start with Lat, LHA, and dec and end up with Hc and Zn. Here we have Lat = 45N, dec = N 19º 23.9', and LHA = 327.  We can find the right answer with the "SR Methods and Fix" tool, shown below, by selecting a direct computation called here "Law of Cosines." 

Enter LHA = GHA and use Lon = 0. Enter dec and Lat and then choose your sight reduction on the right and click it.  Then you have to study the output carefully to see what the individual steps of the solution should be—although this does not really apply to the Law of Cosines solution.

Figure 3 The right answer by direct computation.

This gives the answer of Hc = 52º 34.9' and Hc = 122.3, which is not what was found by the NAO table form shown above because it was not filled out correctly.

Now we look at the option called NASR (Nautical Almanac Sight Reduction) which is these days more commonly called the NAO sight reduction tables, standing for Nautical Almanac Office of the USNO.

Figure 4. The NAO solution (called here NASR).

Referring back to Figure 2, we see that he got the parameter A correct (22º 39'), but then failed to round it properly to 23 in Box 2. The bar in box 2 is a reminder to round these values. Then when transferring the data for F, he changed the 59 to a 39, and so carried on with A = 22 and F = 39 when this should have been A = 23 and F = 59.

Below is the result using wrong input, which was actually extracted properly, followed by the table showing the right values.

Figure 5. NAO Table selection showing student's wrong entry.

Figure 6 Right data from NAO tables.

When these values are used to complete the process the NAO results are Hc = 52º 35 and Hc = 122.3, which is within 0.1' of the best solution. This agreement is better than average. The NAO solution will generally be right on Hc to within ± 0.4' and will usually have the right Zn to a tenth or two.

We encourage everyone who is practicing with sight reduction of Pub 249, Pub 229, NAO or even more exotic older tables to have a look at this tool. It will save you a lot of time.

Here for reference is the same sight reduction done by Pub 229 and then by Pub 249.

Figure 7. Pub 229 solution details.

Figure 8. Pub 249 solution details.  In our cel nav course we interpolate the d-corr in 249, so we may differ by a tenth or two on Hc. He follows the official rules and rounds the declination.

How to Report Nautical Chart Corrections

One great virtue of electronic charts is their ability to be updated quickly by both NOAA's Office of Coast Survey (OCS), who makes the charts, and then the mariners who use them on the water. Electronic Navigational Charts (ENC) are updated weekly by OCS. All type-approved ECDIS (electronic chart display and information system) software as well as many ECS (electronic chart system) used by recreational mariners such as OpenCPN, Coastal Explorer, and Time Zero products offer an automated chart update service built right into the navigation software. 

You can configure the nav programs to check for new charts every time you start the program, or you can update manually. Then if you are online at the time, the program logs into the right NOAA web page, checks for latest charts, and downloads new ones. NOAA provides the needed application programing interface (API) for programmers to use for this.

An important caveat to this process is: for this to work, you must have loaded the charts in the first place using the program's own chart loading function. Most nav programs with the auto-update option have two ways to initially load a chart: select it from a list of charts they provide and then the program gets the charts for you, or it lets you load charts manually by simply telling the program where charts are located on your computer. Loading charts manually can bypass the auto-update functionality. It is important to understand how your own ECS handles these updates. Using OpenCPN, for example, this means using the Chart Downloader plugin for all charts you want to automate, and then store all such charts in the same folder selected in that function.

To illustrate the power of modern chart updating options, we take a look at how mariner's can take part in the process with what is effectively "crowd sourced" chart updating. We will look over the submission process for a user reported chart correction, and then follow through on it showing up in subsequent charts. We posted an earlier article on this process featuring a UKHO app designed for this. The US counterpart described there has since changed to what we show here, but the UKHO app is still available, and as far as we know could still be used to report comments on US charts, although the procedure shown here is the most direct.

What led us to return to this topic is we ran across a prominent naming error on ENC number US4WA11M (Puget Sound, Northern Part) that mis-labeled Montlake Cut at the west end of the Ship Canal that leads from the Puget Sound via the Ballard Locks into Lake Washington. On that chart it was called Montauk Cut—a famous maritime name for sure, but from NYC, not Seattle. Chart US4WA11M is scale 1:80,000, which is within the scale band 5 that spans scales of 1:50,000 to 1:150,000.

Here is the location we discuss within Puget Sound, followed by the object of interest shown on a chart.

This is the object as we first found it, with an insert showing the chart ID. This is viewed in OpenCPN, showing part of the "cursor pick" display seen when right clicking the Cut—this is the way you access object data on an ENC. The more general chart info shown is usually at the bottom of the display, seen with a click on the chart bar.

Montlake Cut can also be seen on scale band 5 chart US5WA13M, which is 1:25,000. If we zoom in to that scale we see that the Cut and Bridge are labeled correctly on that chart, so the only issue is US4WA11M.  

As noted above, at one point NOAA/OCS had a dedicated webpage for reporting chart errors, but they have updated that, now combining chart error reports with their generic page for comments and questions that we find at 

https://www.nauticalcharts.noaa.gov/customer-service/assist/

At this page, we select the Report an Error tab, and then just go down the line of entries.

There is a full NOAA interactive catalog in the right side panel, so you can find the exact Lat-Lon of the error with a button click. You can then include a screenshot of the error. 

I do not know how long the error on US4WA11M was there, but I noted it on Monday, Nov 2, 2020 and sent in that form at about noon, Seattle time.  I was surprised to then get this back at 3:35 PM the same day:

From: NOAA Coast Survey Customer Response for Ticket #148408 

3:35 PM Monday, Nov 2, 2020

Thank you for your inquiry into NOS products.  You are right, the name of the waterway was incorrect on US4WA11.  It has been revised in our database from Montauk Cut to Montlake Cut.  An update for US4WA11 (Edition 41, Update 7) should be available for download within a week.  Again, I'd like to extend my thanks to you for pointing out this error, so that it could be corrected.

Sincerely,

[name given]

Original Message:

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

"Good day, I would like to point out that on US4WA11 the Montlake Cut is misprinted as "Montauk Cut." This does not show up on US5WA13, as noted in the attachments. Please let me know that you have received this, and if you can, please give me an estimate of when we might expect this to be corrected.  Thanks very much. David Burch / Starpath School of Navigation / Seattle"

I am not sure when the actual update was made, but three days later on thursday we checked by doing a chart update for US4WA11M, and found the following:

So we see that it was indeed already fixed!  The new one is edition 41 /7. We can go the charts list to check when it was actually made (see link at www.starpath.com/getcharts):

It looks like the new update was issued on the same day of the report and actually built into the zipped ENC file on the next day. 

I doubt we can expect that type of turn around in general, unless it is a simple one like this one that is easy to see and fix. But they do have the chance to issue a new update every week.

If you see things on a chart that are not right, or you have documented info to improve the charted data, then this is an easy way to submit it. Our feeling has always been that even though the ENC take some practice to get used to, in the end they will be superior to the RNC and offer mariners very much more information about the waterways.

Note added Nov 23:  Another way to follow up on your proposed correction is a new webpage they have on  weekly chart updates: 

https://distribution.charts.noaa.gov/weekly_updates

It takes a bit of practice, but you can look for updates per date nationwide or home in on specific charts or specific weeks.  A nice new edition to these modern times of weekly updates.  This may not be an advertised public site yet, but it is active.

Before submitting your proposed correction, it could be, depending on the correction, useful to check the latest USCG Weekly Notice to Mariners to see if the error has already been reported. And indeed, if the error is potentially hazardous to navigation, you might also report it to the Aids to Navigation office of the local USCG.

We have related ENC notes online at  Naming and Boundary Conventions in ENC.

For more details on the structure and use of ENC, see Introduction to Electronic Chart Navigation.

Into the Weeds with Abbreviations

There is a nuanced twist to navigation terminology that is ever more likely to be confronted... if you might care to ponder such things. It relates to a hierarchy in the specificity of abbreviations. 

mb, Pub., WA are abbreviations. We write them as letters and then read them or pronounce them as the words they stand for, "millibars," "Publication," "Washington."  We can think of these as abbreviations, level 1.

GPS, ENC, COG are initialisms.  They are abbreviations we read and pronounce letter by letter, without saying, or maybe even knowing, what they stand for. We might call these abbreviations, level 2.

And then there is RADAR, ECDIS (pronounced "ekdis"), ATON (pronounced "ay-tahn"), which are acronyms. These are abbreviations that have been elevated to actual words that we pronounce as they are spelled.  Level 3!

Beyond this tidy arrangement, there is at least one loose cannon floating around the nav station.

NMEA, representing the National Marine Electronics Association, is often used as an acronym, which for some unknown reason is commonly pronounced "neema," which has nothing to do with what was once an unambiguous acronym (NIMA) for National Imagery and Mapping Agency  (1996 to 2003) that had replaced the Defense Mapping Agency, known by the initialism DMA.  NIMA was replaced with the NGA, the initialism for National Geospatial Agency, which serves an expanded function today, including the production of many useful nav pubs.

Years ago we proposed the name "erble" be used to elevate the abbreviation for electronic range and bearing line (ERBL) to an acronym. This does make reference to it more tidy,  but I am not sure if this ever caught on much. The longer the abbreviation, the more attractive an acronym becomes.

We got into this abbreviation minutiae today as we prepare our new online course on echart navigation, which focuses on ENC, electronic navigational charts. These are the vector charts that will replace all traditional paper charts and RNC (raster navigational charts) by the end of 2024, which is not that far away — it is now Nov 10, 2020, and many folks are at this moment well aware of  how long 4 years is!

Everything displayed on an ENC is an object, and every object is described by several attributes. Every object on the chart has a 6-letter abbreviation: landmark is LNDMRK, lateral buoy is BOYLAT. We learn what these attributes are when reading an ENC by clicking the object, called a cursor pick, which brings up a list of the objects at that point (usually several) as well as their attributes.

The attributes are also each given a 6-letter abbreviation. Thus, object BOYLAT has attribute BOYSHP (buoy shape), which has 8 possible values; attribute CATLAM (category of the lateral mark), which has 4 possible values; plus attributes for color, color pattern; etc.  There are 27 possible attributes of an object BOYLAT, which you can see defined at this online ENC Object Catalog from Caris.

One of the first things we might note on that wonderful Caris reference, is they call the abbreviations "acronyms." For the most part, this is not right. We might get by with BOYLAT or CATLAM, but what about the crucial object used to describe rocks: UWTROC (underwater/awash rock). The vast majority of the abbreviations for objects and attributes are awkward at best to pronounce. Caris cannot be blamed for their use of the term. The International Hydrographic Organization  standard for ENCs (IHO S-57)  calls them "acronyms."

The point at hand here is that some abbreviations for objects and attributes will nevertheless inevitably become acronyms right out of the box, such as the attribute that nearly all objects have called SCAMIN (scale minimum,  maybe pronounced "ska min"). You must be zoomed into a scale equal to the SCAMIN or larger in order to see the object on an ENC. Recall that chart scales are defined as ratios: 1:40,000 (1/40,000) is a larger scale (fraction) than 1:80,000 (1/80,000). A lateral beacon (BCNLAT) with a SCAMIN of 44,999 will show up on a 1:40,000 display, but will disappear off the chart when you zoom out  to 1:80,000.

But I wander into the charting here, when the topic is abbreviations. The point is this: as we learn more of the 500 ENC objects and the 400 ENC attributes that can be used to describe them, we will first confront the fact that they look the same, each abbreviated with 6 capital letters, then we will most likely bump around a bit as we decide which of these should be honored with acronyms, and if we want an acronym for an abbreviation we can't pronounce, what word do we invent for it—in the spirit of NMEA.  

If we have friends working in the government, we can ask them for help. They are experts at this... think of NOAA (noah), but that is just an ice crystal on the tip of the iceberg of government speak.

For completeness, I might note that the IHO has a standard for what must be in an ENC called IHO S-57 and another standard on how this information should be presented to the mariners, which is called IHO S-52. In the latter they discourage the use of the abbreviations for objects and attributes in lieu of  full names that they refer to as "human readable language." 

Consequently, many echart programs do not use the abbreviations at all, however, my own work with ENC has shown a certain value to having these available. OpenCPN, for example, uses both the abbreviations and the full names for the objects, but only abbreviations for the attributes. Other programs do not use abbreviations at all.

Detecting Fast Winds Aloft... and why we care

The winds aloft at about 500 mb (18,000 ft) play a key role in the winds we ultimately feel on the surface. The relationship is discussed in our textbook Modern Marine Weather. In short, the direction of the winds aloft tell us which way the surface Lows will approach us, and the speed of the winds aloft are a measure of the speed of the surface Lows (about 30 to 50% of the winds aloft speeds) as well as the severity of the surface winds we can expect.  The seminal explanation of the practical relation between winds aloft and surface winds is by Joe Sienkiewicz and Lee Chesneau.

Short of having an actual map of the winds aloft (which is easy to come by if we have wireless connections), we can gage both speed and direction from visual observations. Again, I refer to our text for details, but one way to spot direction is to note that the winds make waves in high cirrus clouds, much as wind makes waves in water. These waves show up as fine ripples in cirrocumulus clouds, called mackerel sky. The direction of the winds are, as is the case with water waves, perpendicular to the waves,  inline with the motion of the waves.

The speed of the winds aloft can be judged from other cirrus cloud patterns, such as prominent mare's tails. The very existence of a prominent and persistent wave pattern is some indication of at least a well defined wind pattern, but a more positive sign is the topic at hand. Namely, if you can actually see the high cirrus clouds moving, then the winds must be fast.  We mention this in several books, but this is not a very common observation, although we do indeed often see cirrocumulus in neat wave patterns.... as if waves in sand—as opposed to the much broader and more common patterns seen in altocumulus waves. 

Note that most internet discussion and many books and some glossaries assign "mackerel sky" to altocumulus patterns, and there is no particular problem with that, but those clouds (waves in altocumulus) are not forecasters of strong winds, and not what was meant in the old saying "Mackerel skies and mare's tails make tall ships set low sails." This refers to  cirrocumulus patterns, indicators of the winds aloft.  Altocumulus patterns are determined mostly by boundary layer winds (~850 mb) that reflect what is going on now, not what is coming over the horizon. 

Actually, let me take that back. There is a problem with the misidentification of the clouds that go with that famous forecasting jingle. Namely it dilutes our ability to do useful onboard forecasting based on what we see alone without weather maps or official forecasts at hand. In short, to use modern jargon, such discussion is fake news that can lead us astray. In any event, once you see that error in place, it is fair warning to be careful about other things stated in that reference. Sometimes we need to make the difficult distinction between high-end altocumulus and cirrrocumulus. See notes at the end about cirrocumulus v. altocumulus cloud waves. The importance of cirrus clouds for forecasting was known in the late 1800's.

The difficulty with spotting the cloud motion at sea is we need a reference to judge the motion by. Here on land, and in the sample below we have a building to use. 

To follow up on this observation, which was made in Seattle at 1700 PDT, Sept 25, 2020, (00z on Sept 26),  we can go to the FTPmail folder of weather maps. Strangely enough, the OPC, which makes these maps, do not post the most recent 500-mb map on their own web page. They include a 24h and 48h forecast instead, but we can get the map valid at 00z 9/26 from the link above. At that link, go to Pacific / Upper Air Charts / 500 mb / Most Recent, which is shown below.... you will of course not see this when you do it as this will no longer be the most recent!

We see that the winds aloft we were viewing to the S at the moment could be as large as some 85 kts (exact values not clear as they are not labeled overhead and I have not tried to compute how far south these were at 40º high in the sky). The model winds on this map, however, are indeed high winds aloft speed (average may be closer to 60), although they can be much higher (>100 kts), but on the average they are lower.  

If we look at the surface analysis at this time, we do not see much activity as shown below.

But the forecasts for the next two days do show a large storm developing in the Gulf of Alaska.

By this time, the winds aloft have backed down to the SW from the westerlies we were observing, a direction you can discern in the surface forecast from the orientation of the isobars in the warm sector of the accompanying frontal wave—and they are predicted to get even faster.

We won't see the effect on high clouds here in Seattle as, our winds aloft will be from the NW at moderate speeds, and we are well sheltered from that Low, but anywhere within that great sweep of the SW winds aloft, S to SE of the Low, should show some pretty dramatic cirrus patterns.

__________________

Cirrocumulus waves vs. Altocumulus waves. 

Here are a couple sample comparisons from the remarkable WMO International Cloud Atlas.

The altocumulus above right are high ones where the identification becomes harder, but this example shows what we often see in altocumulus waves, namely indications of many different wind directions. This is a giveaway that this sky does not reflect the high winds, which will typically present a consistent, unique direction... although all such wave patterns are transitory.