| 24 Sep 2026
Design and Evaluation of a Low-Cost Horizontal Tube Radiation Shield for Temperature and Humidity Measurements in a Tropical Urban Environment
Abstract. Climate change and rapid urbanization have increased the need for dense air temperature and humidity monitoring networks in tropical cities. Although low-cost sensors are widely available, the cost of radiation shields remains a major barrier to large-scale deployment. This study presents a low-cost horizontal tube radiation shield (H-Tube) constructed from commercially available pipes and fittings combined with a small number of 3D-printed components. Two versions were developed: a bright-annealed stainless-steel shield (H-TubeSS) and a PVC shield covered with aluminum foil (H-TubePVC). Material costs were approximately USD 25 and USD 11, respectively, making them about 8 and 18 times less expensive than typical commercial radiation shields (>USD 200).
Performance was evaluated through comparative field experiments in a tropical urban environment in Bandung, Indonesia, using identical Vaisala HMP155A temperature-humidity probes. Measurements from the H-Tube were compared against a Cotton Region Shelter (CRS) reference and two commercial radiation shields: a multiplate (MP) shield and a vertical tube (V-Tube) shield. Under non-aspirated conditions, daytime temperature biases exceeded 4 °C and relative humidity biases exceeded 15% during periods of strong net radiation. In contrast, aspirated operation substantially improved performance, with temperature biases generally remaining within ±1 °C and relative humidity biases within ±5%, comparable to those of the commercial MP and V-Tube shields. The aspirated H-TubeSS achieved a temperature RMSE of 0.49 °C relative to the CRS, comparable to the MP shield (0.53 °C) and slightly lower than the H-TubePVC (0.58 °C).
Simple bias-correction methods based on linear temperature regression and saturation-vapor-pressure adjustment for relative humidity were also developed and evaluated. For the H-Tube designs, temperature RMSE was reduced from 1.35-1.46 °C to approximately 0.56 °C under non-aspirated conditions and from 0.49-0.58 °C to 0.30-0.35 °C under aspirated conditions. Relative humidity RMSE was reduced to approximately 2.6-3.2% after correction. The correction methods also reduced temperature-measurement uncertainty, particularly for the non-aspirated configurations.
These results demonstrate that the aspirated H-Tube provides a practical, scalable, and low-cost alternative to commercial radiation shields for distributed temperature-humidity monitoring networks in tropical urban environments.
Overall comments:
The manuscript lays the foundation for creating a low-cost, horizontal radiation shield for use in urban environments when making Temperature/Relative Humidity measurements. Such shield designs are needed for specific applications and the authors do a good job of designing a reasonable shield that prioritizes their goals. The manuscript is well laid out and presents the findings well. I have a few technical comments related to the design itself that I think bear further consideration.
Major Comments:
1). If other shield designs exist that address some or all of the stated concerns for the tropical urban environment the authors are studying, why not use those? Are there deficiencies in the currently available designs that the authors can state that require designing a new shield? From reading the introduction, my guess would be that the authors are attempting to create a substantially cheaper alternative (admirable and perfectly acceptable goal), but this isn’t clearly stated. I think adding a bit of detail to the introduction that highlights why this need exists could be useful. If the other shields that are available work for example, but are cost prohibitive, that needs to be clearly stated.
2). The double wall design is excellent and practical given the solar heating concerns, but is relatively narrow compared to the size of the HMP155 sensor as the authors state towards the end of the manuscript. This is particularly relevant for the HMP155 as depending on the filter used, this could significantly restrict airflow inside the shield and to the sensor itself. Were there tests done to explore the aspiration rate inside the inner tube or variations on overall size to preserve airflow?
3). The 45 degree angle inlet could potentially allow for wind driven rain to be pushed inside the horizontal section, has this been tested during particularly windy events? I see a wire mesh on the inlet and it’s stated there is one on the outlet. This could restrict airflow further, and for the inlet may provide a space for water to congregate, leading to excessive wetbulb errors
4). Reflected radiation on the inlet could lead to heating of the wire mesh, increasing temperature errors. Upstream thermal mass could modify temperature readings. This may come out more as an error source depending on the environment it is used it, more testing would be required to identify this, but do the authors have any comments regarding whether the wire mesh itself is providing any source of thermal mass?
5). Space for a single sensor does not allow for second faster temperature measurement, leading to slower response time given the time lag of the HMP. During periods of rapid change this will lead to excessive temperature errors and humidity errors. Did the authors consider making a larger diameter version that could accommodate multiple sensors?
6). It is unclear where the cable for the HMP comes out and how this could affect the airflow. Either text or an illustration should be added to make this more clear.
Minor comments:
Line 71-72 – it is true that multiplate shields are sensitive to wind-driven rain, but this statement should have a few references to go with it.