Glossary
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| AOI | Area of Interest |
| BBOX | Bounding Box defined by two longitude and two latitude coordinates. Used for monitoring areas of interest (AOI) like river section, selected farmland, erosion, irrigated land. In case of mathematical monitoring, the size of the BBOX is related to the outcome of monitor calculations. |
| category | Content of this website can be searched by article or subject “category“. Popular categories are ‘flow status’, ‘flow parkhq msembe’, ‘flow mtera’, and ‘alerts’. |
| Core water point | A fixed 25 m² (5 × 5 m) reference point/pixel classified as water or shallow water by the joint-population classifier. Core-water points represent locations with the strongest spectral evidence of surface water, but the presence of water pixels does not by itself establish that the water is flowing. Continuous surface flow requires a continuous channel of surface-water pixels, including water or shallow-water classes, and is assessed through wider visual inspection of the river channel, for example with the interactive Maji Yetu GEE map. At A2, the monitored joint population contains 255 fixed reference points; zero core-water points means that none of those points was classified as water or shallow water. |
| ESA | European Space Agency |
| False Color | A Sentinel-2 composite using Bands 8, 4 and 3 (near-infrared, red and green), typically displaying vegetation in red and water from dark blue to black. The native resolution of these bands is 10 m. In parts of the Maji Yetu river-monitoring workflow the imagery is resampled to 5 m to improve visual inspection of water versus non-water boundaries. Although the 5 m pixels are interpolated from the original 10 m information and therefore do not create new independent spatial information, the finer display provides a smoother representation of the waterline and reduces the strongly stepped appearance of 10 m pixel boundaries, which assists detailed visual interpretation of narrow channels and transition areas. |
| HR | High Resolution. In the Maji Yetu monitoring work, high-resolution imagery, including Google Earth imagery where appropriate, is used as reference imagery for visual verification and calibration. |
| Joint-population pixel analysis | A satellite-monitoring method applied at a selected geometry or monitoring site, in which the same fixed population of reference points is repeatedly classified through time. Changes in the distribution of core-water and transition points are used to monitor the progressive fragmentation and drying of the surface-water channel and to investigate the transition from continuous surface flow to disconnected or stagnant residual water. |
| Joint-Population Zero Flow Observation (Joint-Population ZFO) |
A ZFO derived from the temporal and spatial behaviour of the fixed joint-population reference points. Its criterion must be calibrated against evidence of loss of continuous surface flow; core_water_count = 0 is not itself the definition of Joint-Population ZFO.
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| NBR | Normalized Burn Ratio. A spectral index commonly used for detecting burned areas. In the Maji Yetu monitoring approach it has also proved to be an effective tool for detecting irrigation-related surface changes. The Sentinel-2 NBR products used by Maji Yetu use the readily available near-infrared and short-wave infrared bands and are analysed at their 20 m working resolution without resampling. |
| NDWI | Normalized Difference Water Index: (B03 − B08) / (B03 + B08), or (Green − Near Infrared) / (Green + Near Infrared). NDWI is widely used to distinguish surface water from surrounding vegetation and soil, often using a threshold around NDWI = 0 as an initial water/non-water separation. In the development of the Maji Yetu river-flow monitoring approach, reliance on NDWI as a single threshold value and as a stand-alone method for detecting river flow has gradually been reduced. Water and flow assessment increasingly uses additional spectral, spatial, temporal and visual evidence. |
| RMSE | Root Mean Squared Error |
| SCL | Scene Classification Layer provided with Sentinel-2 Level-2A imagery at 20 m resolution. It classifies pixels into categories such as cloud, vegetation, bare surface and water and can be used for masking, quality control and comparison with spectral water classifications. In the earlier development of the Maji Yetu monitoring approach, SCL was also used as reference information in developing and evaluating NDWI-based water thresholds. Its role has gradually reduced as river-flow assessment has moved away from dependence on a single NDWI threshold toward combined spectral, spatial, temporal and visual evidence. |
| SR | Surface Reflectance. Sentinel-2 Level-2A reflectance corrected for atmospheric effects and representing Bottom-of-Atmosphere (BOA) reflectance. |
| TOA | Top Of Atmosphere reflectance. Sentinel-2 Level-1C imagery represents reflectance measured at the top of the atmosphere, before atmospheric correction to surface reflectance. |
| Transition point | A fixed 25 m² (5 × 5 m) reference point/pixel classified as having mixed or transitional spectral characteristics rather than belonging to the core-water classes. These may include combinations associated with water, vegetation, shallow or dry surfaces, or humid exposed channel surfaces. A transition point is therefore not counted as a core-water point and does not by itself demonstrate surface flow. |
| VDAS | Virtual Drainage Assessment Section of the Ruaha River |
| Visual Remote-Sensing Zero Flow Observation (Visual ZFO) | A ZFO assigned through visual interpretation of remote-sensing imagery according to the criteria used for that historical visual series. The interpretation should extend beyond a narrow AOI wherever imagery allows, so that the continuity of the wider river channel can be assessed. For example, an A2 Visual ZFO should be supported by evidence of interruption of the channel beyond the immediate A2 analysis area, including downstream sections where relevant. The same principle applies when visually assessing Zero Flow in other monitored river sections. |
| Zero-core observation |
A joint-population observation in which no reference point is classified as core water (water or shallow). This is a classifier endpoint and must not be abbreviated ZFO.
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| Zero Flow (ZF) | The physical/hydrological condition in which continuous surface flow through the monitored river channel has ceased. Residual stagnant or disconnected pools may remain. |
| Zero Flow Days — Ruaha River series | The historical Zero Flow Days series refers to observations at the Ruaha River VDAS at Msembe Bridge, close to Ruaha National Park headquarters. It should not automatically be interpreted as the Zero Flow date at A1, A2, Mtera or another monitoring location. |
| Zero Flow Observation (ZFO) | An observation by a specified method that provides evidence that the river has reached Zero Flow. Because it is an observation, its date and criteria depend on the observation method. |