News Archive History:

Wind Sensor Replacement

September 2023 | SLEP Initiative

• The manufacturer of the ASOS Ice Free Wind Sensor, the Vaisala 425NWS, announced in 2016 that 425NWS repair parts were no longer available, rendering the sensor obsolete.

• The awarded logistics replacement to the NWS-425 is the Vaisala WMT-702 with heated tip transducers.

• Testing was performed on the WMT702 at the Sterling Field Support Center and an in-depth data evaluation was conducted at twelve operational ASOS sites in lieu of a formal Operational Test & Evaluation (OT&E).

• The objectives of the evaluation were to evaluate the installation of the sensor, the integrity of the wind data, the representativeness of the wind data as well as the performance of WMT702-equipped ASOS.

• Based on the findings of this  evaluation, it was recommended that the WMT702 be deployed as-needed across the ASOS network.

• Final procurement of sufficient sensors to deploy to all ASOS sites was completed during January of 2023 and the full population of ASOS sites should have a new wind sensor by December 31, 2023.

Air and Dew Point Temperature Sensor Replacement OT&E

August 2023 | SLEP Initiative

• ASOS is a Tri-Agency Program with the Department of Commerce (DOC), Department of Transportation (DOT) and Department of Defense (DoD).

• Sustainment activities for Sensors From 2022 - 2027 must be coordinated across all three agencies.

• The Temperature and Relative Humidity sensors presently fielded with the ASOS, include the DTS-1 and the HO-83/1088, whose designs are well over 20 years old.

• The DTS-1 is no longer supported by Vaisala as of August 31, 2020 and will be unable to be repaired beyond August 2021.  Additionally, the HO-83/1088, is very expensive to maintain and has known reliability issues. 

• The ASOS Program has an approved temperature and dew point sensor replacement design using the HMP-155E dual probe; one for TA (Air Temperature) and one for TD (Dew Point Temperature).

• The sensor probes sense Ta and Relative Humidity to calculate the TD. Some refer to this effort as the TRH project as well.

• This design has been procured with an operational test started in July 2024.

• Updates to this project will be posted as they become available.

Update: Jan 8, 2024

Data errors at the first operational test site required the rollback of the HMP-155E Temp/Dew sensor to the legacy 1088/DTS1 sensors at Annapolis, MD (NAK). This was successfully completed Thursday, December 14, 2023. NAK was fully operational with the legacy sensors as of the 1754 UTC METAR.

Resumption of the Temp/Dew Operational Test will be announced in the near future.

Update: November 20,2023

The NWS announced the commencement of the Air and Dew Point Temperature sensor replacement Operational Test and Evaluation in this public statement. The ASOS Program is now in an Operational Test and Evaluation posture, the following schedule is provided for information.

The first three sites are being installed in between FAA mandated maintenance moratoriums due to the Thanksgiving and Christmas Holidays that will provide the opportunity for the NWS to monitor these three sites through the month of December 2023. The schedule picks back up in January.

The dates provided are target dates with no guarantees of successful installation. Additional information will be provided as it becomes available.

Temperature and Dew Point Sensor Upgrade

September 20, 2023

Procurements for the new Ta/Td (TRH) sensor system are now complete; the components of the system are:

1. Vaisala HMP-155E dual probe Temperature and Relative Humidity sensor with warmed RH probe to prevent condensation with the additional temperature probe. The HMP-155 can measure temperatures as low as -80C (-112F) and as high as +60C (140F). The full specifications can be found here. The full HMP-155 Users Guide is available here.

2. RM Young Solar Radiation Shields will be employed with HMP-155 specific mounting interfaces. The Ta probe will be in the Compact Aspirated Radiation Shield, Model 43502 while the RH Probe will be mounted into the Multi-Plate Radiation Shield, Model 41005-5. 

3. Campbell Scientific will provide the Electronics enclosure and mounting hardware for the replacement system. The HMP-155 and RM Young Radiation Shields will be interfacing with the Legacy ASOS through an electronics enclosure supplying power and processing data into the Data Collection Package. This power supply will be mounted using ASOS standard flange adaptors to existing pedestals and additional mounting hardware to secure the radiation shields in accordance with the Federal Standard for Siting Meteorological Sensors at Airports.

The ASOS Program Office is preparing for Operational Test and Evaluation OT&E) of the new Temp/Dew system beginning in October 2023 for a period of about four months ending in January 2024. Pending successful operational test, operational implementation will follow throughout 2024 and into 2025 at approximately 953 ASOS sites. Once OT&E sites receive and install their new Temp/Dew systems and testing begins, we will announce the sites to the public.