Multi-rotor UAV and gradient tower observations of the atmospheric boundary layer over the eastern Taihang piedmont, Hebei, China (July 2025)

## 1. Overview This dataset contains three complementary sets of atmospheric boundary layer (ABL) observations collected in Hebei Province, North China, in July 2025: | Subset | Files | Platform | Period (Beijing Time, UTC+8) | Resolution ||---|---|---|---|---|| A. Gradient meteorological tower | `2025_07__gradient_meteorological_tower.csv` | 10-level instrumented tower | 2025-07-01 00:00 – 2025-07-31 23:59 | 1 min || B. UAV fixed-level records | `{8,16,32,48,64,80,96}m_profile_up_standard_UAV.txt` (7 files) | Multirotor UAV with meteorological sonde | 2025-07-25 – 2025-07-28 (intermittent flights) | 1 s || C. UAV vertical profile flights | `20250731-profile-{01,02,03}-used_UAV.txt` (3 files) | Multirotor UAV with meteorological sonde | 2025-07-31, 18:24 – 19:56 | 1 s | Subset B was collected at the tower site (37.2904° N, 114.3866° E) with the UAV holding at the nominal tower observation levels (8–96 m AGL), enabling direct UAV–tower intercomparison. Subset C comprises three deep profile flights (up to ~1500 m AGL) at a second site in the western hills (37.8673° N, 114.2618° E). All timestamps in all files are **Beijing Time (UTC+8)** unless noted otherwise. Coordinates are decimal degrees (WGS-84, as reported by the UAV GNSS). --- ## 2. Subset A — Gradient meteorological tower (`2025_07__gradient_meteorological_tower.csv`) **Format:** CSV, **GBK (CP936) encoding** — column headers are in Chinese. The file will appear garbled if read as UTF-8; see the code example in Section 5.**Size:** ~113 MB, 446,400 data rows = 31 days × 1440 min × 10 levels. Missing values are recorded as the literal string `NULL`. Each row is one observation level at one minute. The level identifier is in column `观测层`: | `观测层` code | Level index | Nominal height (m AGL) ||---|---|---|| `DMWD.00001` | 01 (lowest) | || `DMWD.00002.02` | 02 | || `DMWD.00003.03` | 03 | || … | … | … || `DMWD.00010.10` | 10 (highest) | | Levels are ordered bottom-to-top (mean wind speed increases monotonically from level 01 to level 10). Note the lowest level's code lacks the trailing `.NN` suffix that all other levels carry. **Column dictionary** (original Chinese header → meaning, unit): | Column (GBK header) | Meaning | Unit ||---|---|---|| `观测时间` | Observation time (Beijing Time), `YYYY/M/D H:MM` | — || `观测层` | Observation level code (see table above) | — || `2分钟风向` / `10分钟风向` | 2-min / 10-min mean wind direction | ° (from north) || `2分钟风速` / `10分钟风速` | 2-min / 10-min mean wind speed | m s⁻¹ || `10分钟风速标准偏差` | Standard deviation of 10-min wind speed | m s⁻¹ || `10分钟极大风速` | 10-min extreme (instantaneous gust) wind speed | m s⁻¹ || `10分钟最大风速` | 10-min maximum wind speed | m s⁻¹ || `温度平均值` | Mean air temperature | °C || `湿度平均值` | Mean relative humidity | % || `气压平均值` | Mean station pressure — **reported only at level 02**; `NULL` at all other levels | hPa || `U/V/W风速观测值`, `超声虚温观测值` | Sonic anemometer instantaneous u, v, w wind components and sonic virtual temperature — **reported only at level 07**; `NULL` elsewhere | m s⁻¹ / °C || `U/V/W风速10分钟平均值`, `超声虚温10分钟平均值` (+ `…标准偏差`) | Sonic 10-min means and standard deviations (level 07 only) | m s⁻¹ / °C || `U/V/W风速30分钟平均值` … / `U/V/W风速60分钟平均值` … | Sonic 30-min / 60-min means and standard deviations (level 07 only) | m s⁻¹ / °C | --- ## 3. Subset B — UAV fixed-level records (`{H}m_profile_up_standard_UAV.txt`) Seven whitespace-delimited plain-text files, one per nominal height `H` ∈ {8, 16, 32, 48, 64, 80, 96} m AGL, at the tower site. Each file collects **all 1-Hz sonde records acquired while the UAV was at that level**, concatenated across multiple flights on 2025-07-25 to 2025-07-28. During each flight the UAV climbed stepwise past the tower, holding at each level for typically 10–40 s; each such hold appears as one short contiguous segment in the file. The `80m` file differs: it is a single continuous ~22-min hover on 2025-07-25. | File | Records | Flight days ||---|---|---|| `8m_…` | 304 | Jul 27–28 || `16m_…` | 437 | Jul 27–28 || `32m_…` | 442 | Jul 27–28 || `48m_…` | 454 | Jul 26–28 || `64m_…` | 517 | Jul 26–28 || `80m_…` | 1309 | Jul 25 (single continuous hover) || `96m_…` | 1328 | Jul 27–28 | **Rows in `48m` and `64m` files are not strictly time-ordered** (flights were concatenated out of sequence). Always sort by timestamp after reading. **Column specification** (17 whitespace-separated columns, no header): | # | Name | Unit | Notes ||---|---|---|---|| 1–6 | year, month, day, hour, minute, second | — | Beijing Time (UTC+8) || 7 | latitude | ° N | WGS-84 || 8 | longitude | ° E | WGS-84 || 9 | wind direction | ° | from north || 10 | wind speed | m s⁻¹ | || 11 | pressure | hPa | || 12 | air temperature | °C | || 13 | relative humidity | % | || 14 | UAV pitch angle | ° | attitude; used for turbulence index TI = √(pitch² + roll²) || 15 | UAV roll angle | ° | attitude || 16 | UAV heading (yaw) | ° | 0–360, from north || 17 | supply voltage | V | constant 23.4 in these files | Geometric altitude is not recorded; the nominal level is given by the filename. Height can also be cross-checked from pressure against the tower level-02 barometer. --- ## 4. Subset C — UAV vertical profile flights (`20250731-profile-{01,02,03}-used_UAV.txt`) Three profile flights at the western-hills site (37.8673° N, 114.2618° E) on the evening of 2025-07-31 (Beijing Time). Each file is the raw 1-Hz sonde stream for one complete flight (stepwise ascent, then descent), with interleaved plain-text **waypoint marker lines**. | File | Data records | Time (BJT) | Max waypoint (m AGL) | Surface / min pressure (hPa) ||---|---|---|---|---|| `…profile-01…` | 420 | 18:24:36 – 18:43:36 | 1500 | 957.0 / 824.9 || `…profile-02…` | 981 | 18:55:41 – 19:22:27 | 1490 | 956.9 / 825.5 || `…profile-03…` | 739 | 19:33:22 – 19:55:56 | 1300 | 973.6 / 843.7 | **Two line types:** 1. **Marker lines** — `Pnn,<target>m,up|down`, e.g. `P02,400m,up`. Written when the UAV was commanded to the next waypoint altitude (m AGL); `up`/`down` distinguishes the ascent and descent legs. Profile 01 additionally contains one annotated marker, `P01,500m,up,解限高,数据亦可用` ("altitude limit unlocked, data remain usable"). Ascent waypoints are spaced 100–200 m apart; the UAV paused briefly at each. Treat these lines as segment metadata, not data. 2. **Data records** — one per second, `#`-prefixed, fixed field labels: ```# 20001 20250731182436 lat: 37.86736679 N lon:114.26181793 E A Wd:202 Ws: 1.42 P: 957.0 T: 27.77 H: 66.2 F: -2.13 H: 1.07 F: 19.78V:23.4``` | Field | Meaning | Unit ||---|---|---|| `20001` | Sonde ID | — || `20250731182436` | Timestamp `YYYYMMDDHHMMSS`, Beijing Time | — || `lat:` / `lon:` | Latitude / longitude (WGS-84) | ° || `Wd:` | Wind direction | ° || `Ws:` | Wind speed | m s⁻¹ || `P:` | Pressure | hPa || `T:` | Air temperature | °C || `H:` (first) | Relative humidity | % || `F:` (first) | UAV pitch angle | ° || `H:` (second) | UAV roll angle | ° || `F:` (second) | UAV heading (yaw), 0–360° | ° || `V:` | Supply voltage (note: no space before `V:` in the raw stream) | V |