2019年8月16日，美国海鸟公司研究与开发部主任David Murphy先生向国际Argo指导组联合主席及其全体成员推送电子邮件，宣称由于Garmin公司生产的GPS接收器存在技术缺陷，在未来某个时间段内，装配该接收器的自动剖面浮标有可能无法正常获取卫星定位信息。受此故障影响的剖面浮标主要涉及美国海鸟公司生产的NAVIS型和Teledyne Webb研究公司生产的APEX型，而法国NKE公司生产的PROVOR/ARVOR型和美国斯克利普斯海洋研究所或MRV公司制造的SOLO型浮标，则未受影响。据报，引起该技术故障的原因与GPS系统用于存储周数的字节数不足有关，设计时仅允许存储最大为1024的周数；然后，至2019年4月6日，GPS系统已经进行了两次数位清零，而Garmin公司生产的GPS接收器却忽略了这一问题。
目前，包括海鸟公司、Teledyne Webb研究公司和华盛顿大学等美国多家研制自动剖面浮标的生产商和科研院校，正在密切关注该技术问题所带来的影响，并展开相关测试工作，以寻求解决方案。而对于那些还未布放、且安装了Garmin GPS接收器的APEX和NAVIS型剖面浮标，生产商也正在考虑召回、修复。
附美国海鸟公司David Mruphy先生和美国华盛顿大学Steve Riser教授邮件原文如下，敬请关注！
This week a firmware bug was reported in the Garmin GPS receiver that is used in Navis and Apex floats. This email describes the bug and discusses the impact to deployed floats.
Summary of problem:
Each GPS receiver keeps an almanac of information about the GPS satellites that is updated when the receiver connects with the satellites to measure a position.
The almanac contains information about the position and status of each satellite and this information is used to configure the data acquisition of the GPS receiver.
The GPS system counts weeks to a maximum of 1024 counts ( 0 to 1023). The original week 0 was 12:00 am, January 6, 1980, every 1024 weeks the counter rolls over to 0 again. A recent roll over to 0 took place on April 6, 2019. Each satellite entry in the almanac is time stamped with this week count and when an almanac entry is received it is compared to the one currently stored and if the received one has a lower week count than the stored one the received one is discarded.
This is where the firmware bug has effect. An example would be if a stored almanac entry is week stamped 1023 and the counter rolls over the next almanac entry would have week stamp 0 and would be discarded because 1023 > 0. When this happens the almanac will never be updated and the GPS receiver will configure data acquisition based on old information.
The current thought about the impact of this is that GPS positions would be measured with less than all the available satellites and that the time for a float to measure a position would grow longer.
Garmin is working to understand the how out of date almanacs will effect performance in the long term.
What Sea-Bird is doing in collaboration with Dana Swift of UW:
To understand the magnitude of the position error as time goes on we are looking through our pile of old GPS boards to find old almanac files which we will download. We have also asked Garmin to provide historic almanacs. We have an antenna on top of Sea-Bird’s building and we will do A-B-A testing with current and old almanac files. Comparing positions of Sea-Bird using historic almanacs may give us an idea of the impact to performance we will see in the field.
We have also searched our float data base (all existing Navis) to look for a drop in satellites acquired and for longer than usual times to acquire a fix. We have found no difference in performance since the counter rolled over on April 6th of this year.
To avoid interrupted shipments we will download a current almanac into each float’s GPS before shipping, guaranteeing that the float’s GPS will update the almanac appropriately. Teledyne Webb is also planning to do this.
Sea-Bird is still working out how to apply this procedure to the floats that are not deployed but are in the hands of customers, Tom Mitchell or I will advise you when we have made a plan.
Director of Research and Development
13431 NE 20th Street
Bellevue, WA 98005
+1 425 644 3226
Dear Argo Colleagues,
As some of you might know, last week a problem with floats having a GPS unit manufactured by Garmin was discovered. This was reported by the Garmin factory to several float users and producers. This problem affects Teledyne/Webb Apex floats and SeaBird Navis floats.
The problem does not affect SIO or MRV SOLO floats or floats manufactured by NKE. It is unknown how this problem affects floats produced by other manufacturers.
The nature of this problem is well-outlined in the accompanying message (below) from Dave Murphy of SeaBird. All Teledyne/Webb and SeaBird floats presently deployed are affected. In the worst-case scenario, the result of the problem is that these floats will be unable to obtain a GPS fix at some time in the future. It is unknown when that time might be; originally Garmin thought this could happen in the next few months, but subsequent estimates suggest that possibility of much longer times, or the possibility that this might not occur at all. Both SeaBird and UW have conducted tests using various GPS units over the past weekend, with mixed results. In most cases the problem does not appear before times of several years after deployment (if at all), although in a few cases it appears sooner. It is worth noting that this bug was triggered in April of this year and has now been active for several months, but we know of no floats that have yet been affected. There is a straightforward fix for the Garmin bug for floats that have not yet been deployed. We are beginning the process of applying this fix to our floats at UW.
Each individual float group will have to determine how to handle this problem. The float manufacturers are formulating procedures to deal with this and are in the process of contacting their customers with the appropriate information. For floats already on vessels and awaiting deployment, each group will have to make a decision of whether to deploy the floats or to recall them and participate with the manufacturer in fixing them.
The details of the nature of this problem are given in the accompanying message from Dave Murphy. We hope that ultimately this will not have a major impact on the float array, but at this time it is unclear what the effect might be.
University of Washington