skip to main content

Search for: All records

Creators/Authors contains: "Qiao, Na"

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    Most fog detection from space cannot differentiate fog and low stratus clouds, and cannot estimate fog deposition. This study assessed the feasibility of using spaceborne lidar observations from the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) in fog detection and estimation. We tested the method in the central Namib Desert, Namibia, where frequent fog events occur and fog observations are available. Results showed the CALIPSO backscatter signal at 532 nm can differentiate low clouds and fog due to its high‐resolution vertical profiles. Backscatter signals during fog events were significantly higher than those during non‐fog periods. TheR2between backscatter signals and fog observations was 0.85. Moreover, the backscatter signal was also sensitive to relative humidity variation (R2 = 0.66). These results indicate that the CALIPSO data are feasible to estimate fog occurrence and deposition, providing a new perspective for space‐based fog studies.

    more » « less
  2. Abstract

    Monitoring dryland vegetation trends and examining the drivers are of great importance to understand the dryland vegetation response to future climate changes. Recent findings through satellite data indicate that vegetation greenness has increased in several regions worldwide. These greening patterns are driven by human activities or combined human activities and environmental factors. However, the analyses of greenness trend for regions without direct human activities and shrub expansion in drylands are still lacking. To this end, this study investigates the vegetation trend across the Namib sand sea over March 2000 to December 2018 using monthly Normalized Difference Vegetation Index (NDVI) and examines several potential drivers including precipitation, temperature and atmospheric CO2concentration. For the NDVI time series across the whole study region, a significant greening trend was found over March 2000 to September 2012 based on Mann–Kendall test but not over the whole study period. Structural equation modelling results indicated that precipitation and CO2were the dominant drivers of greening. Temperature showed negative effects on vegetation greenness, indicating warming would reduce plant growth in the study region. Spatially, 75% of the region showed statistically significant greening over March 2000 to September 2012 and 39.30% for March 2000 to December 2018. The different vegetation trend results between the entire region and the pixel scale implied that location‐specific greening could be masked by an overall trend. Our study suggested that precipitation (especially the large episodic precipitation events) and CO2are dominant drivers of the observed greening in the Namib. Our findings fill an important knowledge gap of vegetation dynamics in regions without direct human activities.

    more » « less
  3. Abstract

    Fog is an important water source for many ecosystems, especially in drylands. Most fog‐vegetation studies focus on individual plant scale; the relationship between fog and vegetation function at larger spatial scales remains unclear. This hinders an accurate prediction of climate change impacts on dryland ecosystems. To this end, we examined the effect of fog on vegetation utilizing both optical and microwave remote sensing‐derived vegetation proxies and fog observations from two locations at Gobabeb and Marble Koppie within the fog‐dominated zone of the Namib Desert. Significantly positive relationships were found between fog and vegetation attributes from optical data at both locations. The positive relationship was also observed for microwave data at Gobabeb. Fog can explain about 10%–30% of variability in vegetation proxies. These findings suggested that fog impacts on vegetation can be quantitatively evaluated from space using remote sensing data, opening a new window for research on fog‐vegetation interactions.

    more » « less